feat: add scoped theme builder system with per-route, per-module, and multi-site support

- Add theme_scopes and theme_scope_values database tables for scoped themes
- Implement theme resolver engine with inheritance: global > site > module > route
- Add module detection for 20+ routes (shop, guilds, radio, news, etc.)
- Create admin UI at /admin/theme-builder with scope tree and color editor
- Add ScopedThemeVars component for injecting scoped CSS via data-attributes
- Add ThemeScopeDetector client component for runtime module/route detection
- Add site-resolver for multi-site domain detection
- Add /api/themes/export endpoint (JSON, CSS, variables formats)
- Add /api/themes/export/embed.js for external integration widget
- Add server actions for full CRUD on scopes and theme values
- Add admin nav link and EN/NL translations

src/lib/admin-nav.ts

@@ -553,6 +553,12 @@ export const ADMIN_NAV_GROUPS: AdminNavGroup[] = [
 				icon: Sparkles,
 				permission: PERMS.SETTINGS_VIEW,
 			},
+			{
+				href: "/admin/theme-builder",
+				labelKey: "themeBuilder",
+				icon: Palette,
+				permission: PERMS.SETTINGS_VIEW,
+			},
 			{
 				href: "/admin/maintenance",
 				labelKey: "maintenance",