feat: implement theme selection and system integration

vite-frontend/src/themes/loader.ts

@@ -0,0 +1,36 @@
+/**
+ * Theme Loader — auto-registers all built-in themes
+ * ==================================================
+ * Import this module once at app startup (in provider.tsx or App.tsx).
+ *
+ * To add a new theme:
+ * 1. Create a folder under `src/themes/` (e.g. `src/themes/my-theme/`)
+ * 2. Export a `ThemePackage` as the default export from `index.ts`
+ * 3. Import and register it below
+ */
+
+import { registerTheme } from "./registry";
+
+// ── Built-in themes ──────────────────────────────────────────────────────────
+import defaultTheme from "./default";
+import cyberpunkTheme from "./example-cyberpunk";
+
+// Register all themes
+registerTheme(defaultTheme);
+registerTheme(cyberpunkTheme);
+
+/*
+ * ── ADDING YOUR OWN THEME ──────────────────────────────────────────────────
+ *
+ * 1. Create your theme folder:
+ *      src/themes/my-awesome-theme/
+ *        ├── index.ts          ← exports ThemePackage
+ *        ├── components/       ← optional component overrides
+ *        └── ...
+ *
+ * 2. Import and register here:
+ *      import myTheme from "./my-awesome-theme";
+ *      registerTheme(myTheme);
+ *
+ * That's it! The theme will appear in the theme picker.
+ */