fix(theming): restore gruvbox as default via Default() helper

internal/tui/state.go

@@ -54,10 +54,7 @@ func NewWizardState(cfg config.Config, reg *module.Registry) WizardState {
 	}
 	sort.Slice(choices, func(i, j int) bool { return choices[i].ID < choices[j].ID })
 
-	var theme string
-	if list := theming.List(); len(list) > 0 {
-		theme = list[0].ID
-	}
+	theme := theming.Default().ID
 	if override, ok := cfg.ThemeOverrides["__active"]; ok && override != "" {
 		theme = override
 	}

internal/tui/state_test.go

@@ -35,7 +35,7 @@ func TestNewWizardStatePreTicksAllByDefault(t *testing.T) {
 			t.Errorf("%s not selected", m.ID)
 		}
 	}
-	if s.ThemeID != theming.List()[0].ID {
+	if s.ThemeID != theming.Default().ID {
 		t.Errorf("theme = %q", s.ThemeID)
 	}
 }