feat(theming): integrate NvChad chadrc rewrite into Apply

internal/theming/theming_test.go

@@ -117,3 +117,34 @@ func TestApplyPreservesOtherOverlayKeys(t *testing.T) {
 		t.Fatalf("active theme missing after preserve: %s", data)
 	}
 }
+
+func TestApplyRewritesChadrcIfPresent(t *testing.T) {
+	home := t.TempDir()
+	t.Setenv("HOME", home)
+	nvimCfg := filepath.Join(home, ".config", "nvim", "lua")
+	if err := os.MkdirAll(nvimCfg, 0o755); err != nil {
+		t.Fatal(err)
+	}
+	if err := os.WriteFile(filepath.Join(nvimCfg, "chadrc.lua"),
+		[]byte(`M.base46 = { theme = "onedark" }`), 0o644); err != nil {
+		t.Fatal(err)
+	}
+	if err := Apply(config.Config{}, "gruvbox"); err != nil {
+		t.Fatal(err)
+	}
+	data, _ := os.ReadFile(filepath.Join(nvimCfg, "chadrc.lua"))
+	if !strings.Contains(string(data), `theme = "gruvbox"`) {
+		t.Fatalf("chadrc not rewritten: %s", data)
+	}
+	if strings.Contains(string(data), `theme = "onedark"`) {
+		t.Fatalf("old theme still present: %s", data)
+	}
+}
+
+func TestApplyNoChadrcIsFine(t *testing.T) {
+	home := t.TempDir()
+	t.Setenv("HOME", home)
+	if err := Apply(config.Config{}, "gruvbox"); err != nil {
+		t.Fatal(err)
+	}
+}