refactor: retire tui.BuiltinThemes in favor of theming.List

Make internal/theming.List the single source of truth for themes:

- Drop tui.BuiltinThemes, tui.ThemeByID, and the NvChadTheme field on
  tui.Theme. tui.Theme is now a thin {ID, Name} display value.
- Wizard populates its dropdown from theming.List() and uses
  DisplayName for the label.
- neovim.resolvedTheme uses theming.Get (with theming.List()[0] as a
  fallback) instead of a caller-supplied []tui.Theme slice.
- neovim.New signature loses the themes []tui.Theme parameter; update
  cmd/archduino/main.go and all neovim tests to match.

Break the resulting neovim→theming import cycle (theming previously
imported neovim for WriteChadrc) by inverting the dependency:
theming exposes a ChadrcWriter function hook, and neovim registers
its WriteChadrc into it via package init. The theming test stubs
ChadrcWriter directly to exercise the chadrc-rewrite branch without
pulling neovim in and re-creating the cycle.

Delete the now-obsolete TestBuiltinThemesCarryNvChadName / TestThemeByID*
tests in internal/tui/state_test.go — their coverage lives in the
theming package's own tests.

cmd/archduino/main.go

@@ -57,7 +57,7 @@ func buildRegistry(cfg config.Config, themeID string) (*module.Registry, error)
 		themes.New(cfg.Themes),
 		arduinocli.New(cfg.ArduinoCLI, runner),
 		shellconfig.New(cfg.ShellConfig),
-		neovim.New(cfg.Neovim, themeID, tui.BuiltinThemes, pm, git),
+		neovim.New(cfg.Neovim, themeID, pm, git),
 		renode.New(cfg.Renode, pm, yay),
 	}
 	for _, m := range mods {

internal/modules/neovim/neovim.go

@@ -17,12 +17,19 @@ import (
 	"github.com/MDietermann/ArduinoArchSetup/internal/config"
 	"github.com/MDietermann/ArduinoArchSetup/internal/module"
 	"github.com/MDietermann/ArduinoArchSetup/internal/platform"
-	"github.com/MDietermann/ArduinoArchSetup/internal/tui"
+	"github.com/MDietermann/ArduinoArchSetup/internal/theming"
 )
 
 //go:embed assets/*
 var assets embed.FS
 
+// Register WriteChadrc with the theming package so theming.Apply can
+// rewrite chadrc.lua on theme changes without importing this package
+// (which would be a cycle: neovim imports theming).
+func init() {
+	theming.ChadrcWriter = WriteChadrc
+}
+
 // assetMap lists each asset and its destination under ~/.config/nvim.
 // Order matters: Detect iterates in this order and Apply writes in this order.
 var assetMap = []struct {
@@ -40,14 +47,13 @@ var assetMap = []struct {
 type Module struct {
 	cfg     config.NeovimConfig
 	themeID string
-	themes  []tui.Theme
 	pm      platform.PackageManager
 	git     platform.GitClient
 }
 
 // New constructs a Neovim Module.
-func New(cfg config.NeovimConfig, themeID string, themes []tui.Theme, pm platform.PackageManager, git platform.GitClient) Module {
-	return Module{cfg: cfg, themeID: themeID, themes: themes, pm: pm, git: git}
+func New(cfg config.NeovimConfig, themeID string, pm platform.PackageManager, git platform.GitClient) Module {
+	return Module{cfg: cfg, themeID: themeID, pm: pm, git: git}
 }
 
 type state struct {
@@ -79,11 +85,11 @@ func nvimCfg() (string, error) {
 }
 
 func (m Module) resolvedTheme() string {
-	if t, ok := tui.ThemeByID(m.themes, m.themeID); ok && t.NvChadTheme != "" {
+	if t, ok := theming.Get(m.themeID); ok && t.NvChadTheme != "" {
 		return t.NvChadTheme
 	}
-	if len(m.themes) > 0 {
-		return m.themes[0].NvChadTheme
+	if list := theming.List(); len(list) > 0 && list[0].NvChadTheme != "" {
+		return list[0].NvChadTheme
 	}
 	return "gruvbox"
 }

internal/modules/neovim/neovim_test.go

@@ -10,7 +10,6 @@ import (
 	"github.com/MDietermann/ArduinoArchSetup/internal/config"
 	"github.com/MDietermann/ArduinoArchSetup/internal/module"
 	"github.com/MDietermann/ArduinoArchSetup/internal/platform"
-	"github.com/MDietermann/ArduinoArchSetup/internal/tui"
 )
 
 type fakeRunner struct {
@@ -58,7 +57,7 @@ func TestDetectFreshSystem(t *testing.T) {
 	home := t.TempDir()
 	t.Setenv("HOME", home)
 	r := &fakeRunner{installed: map[string]bool{}}
-	m := New(config.NeovimConfig{NvChadStarterRepo: "https://x/starter"}, "gruvbox", tui.BuiltinThemes, platform.NewPacman(r), platform.GitClient{Runner: r})
+	m := New(config.NeovimConfig{NvChadStarterRepo: "https://x/starter"}, "gruvbox", platform.NewPacman(r), platform.GitClient{Runner: r})
 	st, err := m.Detect(context.Background())
 	if err != nil {
 		t.Fatal(err)
@@ -81,7 +80,7 @@ func TestDetectNonNvChadTriggersBackup(t *testing.T) {
 	os.MkdirAll(filepath.Join(home, ".config", "nvim", "lua"), 0o755)
 	os.WriteFile(filepath.Join(home, ".config", "nvim", "lua", "plugins.lua"), []byte("-- lazyvim"), 0o644)
 	r := &fakeRunner{installed: map[string]bool{}}
-	m := New(config.NeovimConfig{NvChadStarterRepo: "https://x/starter"}, "gruvbox", tui.BuiltinThemes, platform.NewPacman(r), platform.GitClient{Runner: r})
+	m := New(config.NeovimConfig{NvChadStarterRepo: "https://x/starter"}, "gruvbox", platform.NewPacman(r), platform.GitClient{Runner: r})
 	st, _ := m.Detect(context.Background())
 	if !st.(state).BackupNeeded {
 		t.Fatal("expected BackupNeeded=true")
@@ -92,7 +91,7 @@ func TestPlanApplyInstallsEverything(t *testing.T) {
 	home := t.TempDir()
 	t.Setenv("HOME", home)
 	r := &fakeRunner{installed: map[string]bool{}}
-	m := New(config.NeovimConfig{NvChadStarterRepo: "https://x/starter"}, "dracula", tui.BuiltinThemes, platform.NewPacman(r), platform.GitClient{Runner: r})
+	m := New(config.NeovimConfig{NvChadStarterRepo: "https://x/starter"}, "dracula", platform.NewPacman(r), platform.GitClient{Runner: r})
 	st, _ := m.Detect(context.Background())
 	p, _ := m.Plan(context.Background(), st)
 	if len(p.Actions) == 0 {
@@ -150,7 +149,7 @@ func TestPlanAfterApplyIsEmpty(t *testing.T) {
 	home := t.TempDir()
 	t.Setenv("HOME", home)
 	r := &fakeRunner{installed: map[string]bool{"neovim": true}}
-	m := New(config.NeovimConfig{NvChadStarterRepo: "https://x/starter"}, "gruvbox", tui.BuiltinThemes, platform.NewPacman(r), platform.GitClient{Runner: r})
+	m := New(config.NeovimConfig{NvChadStarterRepo: "https://x/starter"}, "gruvbox", platform.NewPacman(r), platform.GitClient{Runner: r})
 	st, _ := m.Detect(context.Background())
 	p, _ := m.Plan(context.Background(), st)
 	_ = m.Apply(context.Background(), p, nopReporter{})
@@ -165,14 +164,16 @@ func TestUnknownThemeFallsBackToFirst(t *testing.T) {
 	home := t.TempDir()
 	t.Setenv("HOME", home)
 	r := &fakeRunner{installed: map[string]bool{"neovim": true}}
-	m := New(config.NeovimConfig{NvChadStarterRepo: "https://x/starter"}, "does-not-exist", tui.BuiltinThemes, platform.NewPacman(r), platform.GitClient{Runner: r})
+	m := New(config.NeovimConfig{NvChadStarterRepo: "https://x/starter"}, "does-not-exist", platform.NewPacman(r), platform.GitClient{Runner: r})
 	st, _ := m.Detect(context.Background())
 	p, _ := m.Plan(context.Background(), st)
 	if err := m.Apply(context.Background(), p, nopReporter{}); err != nil {
 		t.Fatal(err)
 	}
 	chadrc, _ := os.ReadFile(filepath.Join(home, ".config", "nvim", "lua", "chadrc.lua"))
-	if !strings.Contains(string(chadrc), `theme = "gruvbox"`) {
+	// Unknown theme IDs fall back to the first entry of theming.List(),
+	// which is sorted alphabetically by ID (currently "catppuccin").
+	if !strings.Contains(string(chadrc), `theme = "catppuccin"`) {
 		t.Fatalf("fallback theme not applied: %s", chadrc)
 	}
 }

internal/theming/theming.go

@@ -13,11 +13,17 @@ import (
 	"strings"
 
 	"github.com/MDietermann/ArduinoArchSetup/internal/config"
-	"github.com/MDietermann/ArduinoArchSetup/internal/modules/neovim"
 	"github.com/MDietermann/ArduinoArchSetup/internal/platform"
 	"gopkg.in/yaml.v3"
 )
 
+// ChadrcWriter is the hook used by Apply to rewrite NvChad's chadrc.lua
+// after a theme change. The neovim module registers its WriteChadrc here
+// via an init() function to avoid a theming→neovim import cycle (neovim
+// now imports theming to look up the NvChad theme name). If nil, Apply
+// skips the chadrc update silently.
+var ChadrcWriter func(nvChadThemeName string) error
+
 //go:embed assets
 var assetsFS embed.FS
 
@@ -146,8 +152,10 @@ func Apply(cfg config.Config, themeID string) error {
 		return fmt.Errorf("update overlay: %w", err)
 	}
 
-	if err := neovim.WriteChadrc(th.NvChadTheme); err != nil {
-		return fmt.Errorf("update chadrc: %w", err)
+	if ChadrcWriter != nil {
+		if err := ChadrcWriter(th.NvChadTheme); err != nil {
+			return fmt.Errorf("update chadrc: %w", err)
+		}
 	}
 
 	// Clear NvChad's base46 theme cache so the new theme activates on next

internal/theming/theming_test.go

@@ -129,6 +129,17 @@ func TestApplyRewritesChadrcIfPresent(t *testing.T) {
 		[]byte(`M.base46 = { theme = "onedark" }`), 0o644); err != nil {
 		t.Fatal(err)
 	}
+
+	// The real ChadrcWriter lives in the neovim package, which cannot be
+	// imported here without creating an import cycle (neovim→theming).
+	// Stub it with a minimal writer that covers what the test asserts.
+	prev := ChadrcWriter
+	t.Cleanup(func() { ChadrcWriter = prev })
+	ChadrcWriter = func(name string) error {
+		return os.WriteFile(filepath.Join(nvimCfg, "chadrc.lua"),
+			[]byte(`theme = "`+name+`"`), 0o644)
+	}
+
 	if err := Apply(config.Config{}, "gruvbox"); err != nil {
 		t.Fatal(err)
 	}

internal/tui/state.go

@@ -5,35 +5,15 @@ import (
 
 	"github.com/MDietermann/ArduinoArchSetup/internal/config"
 	"github.com/MDietermann/ArduinoArchSetup/internal/module"
+	"github.com/MDietermann/ArduinoArchSetup/internal/theming"
 )
 
-// Theme is a named colorscheme presented in the wizard. Each entry carries
-// per-tool theme names; Plan 3b uses NvChadTheme, later plans add more.
+// Theme is a named colorscheme presented in the wizard. It is a thin
+// display value for the dropdown; the authoritative theme catalogue lives
+// in the theming package (theming.List / theming.Get).
 type Theme struct {
-	ID          string
-	Name        string
-	NvChadTheme string
-}
-
-// BuiltinThemes is the fixed list the wizard shows. Keep in sync with the
-// themes shipped by Plan 3's theme module.
-var BuiltinThemes = []Theme{
-	{ID: "gruvbox", Name: "Gruvbox Dark", NvChadTheme: "gruvbox"},
-	{ID: "catppuccin", Name: "Catppuccin Mocha", NvChadTheme: "catppuccin"},
-	{ID: "tokyonight", Name: "Tokyo Night", NvChadTheme: "tokyonight"},
-	{ID: "nord", Name: "Nord", NvChadTheme: "nord"},
-	{ID: "dracula", Name: "Dracula", NvChadTheme: "dracula"},
-}
-
-// ThemeByID returns the Theme with the given ID. The bool is false when no
-// match is found; callers decide whether to fall back or error.
-func ThemeByID(themes []Theme, id string) (Theme, bool) {
-	for _, t := range themes {
-		if t.ID == id {
-			return t, true
-		}
-	}
-	return Theme{}, false
+	ID   string
+	Name string
 }
 
 // ModuleChoice is one row in the module selector.
@@ -74,7 +54,10 @@ func NewWizardState(cfg config.Config, reg *module.Registry) WizardState {
 	}
 	sort.Slice(choices, func(i, j int) bool { return choices[i].ID < choices[j].ID })
 
-	theme := BuiltinThemes[0].ID
+	var theme string
+	if list := theming.List(); len(list) > 0 {
+		theme = list[0].ID
+	}
 	if override, ok := cfg.ThemeOverrides["__active"]; ok && override != "" {
 		theme = override
 	}

internal/tui/state_test.go

@@ -6,6 +6,7 @@ import (
 
 	"github.com/MDietermann/ArduinoArchSetup/internal/config"
 	"github.com/MDietermann/ArduinoArchSetup/internal/module"
+	"github.com/MDietermann/ArduinoArchSetup/internal/theming"
 )
 
 type fakeModule struct{ id, name, desc string }
@@ -34,7 +35,7 @@ func TestNewWizardStatePreTicksAllByDefault(t *testing.T) {
 			t.Errorf("%s not selected", m.ID)
 		}
 	}
-	if s.ThemeID != BuiltinThemes[0].ID {
+	if s.ThemeID != theming.List()[0].ID {
 		t.Errorf("theme = %q", s.ThemeID)
 	}
 }
@@ -71,30 +72,3 @@ func TestSelectedIDsOnlyReturnsChecked(t *testing.T) {
 	}
 }
 
-func TestBuiltinThemesCarryNvChadName(t *testing.T) {
-	for _, th := range BuiltinThemes {
-		if th.NvChadTheme == "" {
-			t.Errorf("theme %q has empty NvChadTheme", th.ID)
-		}
-	}
-}
-
-func TestThemeByIDReturnsMatch(t *testing.T) {
-	got, ok := ThemeByID(BuiltinThemes, "dracula")
-	if !ok {
-		t.Fatal("dracula should exist")
-	}
-	if got.ID != "dracula" {
-		t.Fatalf("got id=%q", got.ID)
-	}
-	if got.NvChadTheme == "" {
-		t.Fatal("NvChadTheme empty")
-	}
-}
-
-func TestThemeByIDFallsBackWhenUnknown(t *testing.T) {
-	_, ok := ThemeByID(BuiltinThemes, "does-not-exist")
-	if ok {
-		t.Fatal("unknown id should report ok=false")
-	}
-}

internal/tui/wizard/wizard.go

@@ -10,6 +10,7 @@ import (
 	"github.com/charmbracelet/huh"
 
 	"github.com/MDietermann/ArduinoArchSetup/internal/module"
+	"github.com/MDietermann/ArduinoArchSetup/internal/theming"
 	"github.com/MDietermann/ArduinoArchSetup/internal/tui"
 )
 
@@ -23,9 +24,10 @@ func Run(ctx context.Context, reg *module.Registry, initial tui.WizardState) (tu
 		return s, false, nil
 	}
 
-	themeOptions := make([]huh.Option[string], 0, len(tui.BuiltinThemes))
-	for _, t := range tui.BuiltinThemes {
-		themeOptions = append(themeOptions, huh.NewOption(t.Name, t.ID))
+	themes := theming.List()
+	themeOptions := make([]huh.Option[string], 0, len(themes))
+	for _, t := range themes {
+		themeOptions = append(themeOptions, huh.NewOption(t.DisplayName, t.ID))
 	}
 
 	moduleOptions := make([]huh.Option[string], 0, len(s.Modules))