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/messages/nl.json

@@ -2850,6 +2850,7 @@
 					"autoDj": "Auto DJ",
 					"cms": "CMS",
 					"theme": "Thema",
+					"themeBuilder": "Thema Bouwer",
 					"maintenance": "Onderhoud",
 					"favicon": "Favicon",
 					"emulator": "Emulator",