feat: collab sub-feature toggles and provider icons

- Add admin toggles for individual collab sections (Chat, Notes,
  Polls, What's Next) stored in app_settings
- CollabPanel adapts layout dynamically: chat always fixed 380px,
  remaining panels share space equally
- Mobile: disabled tabs are hidden
- Add Immich and Synology Photos SVG icons to photo provider toggles
- Add Luggage icon to bag tracking sub-toggle
- API: GET/PUT /admin/collab-features endpoints
- i18n: all 15 languages updated

Closes #604

server/src/app.ts

@@ -45,6 +45,7 @@ import publicConfigRoutes from './routes/publicConfig';
 import { mcpHandler } from './mcp';
 import { Addon } from './types';
 import { getPhotoProviderConfig } from './services/memories/helpersService';
+import { getCollabFeatures } from './services/adminService';
 
 export function createApp(): express.Application {
   const app = express();
@@ -236,6 +237,7 @@ export function createApp(): express.Application {
     }
 
     res.json({
+      collabFeatures: getCollabFeatures(),
       addons: [
         ...addons.map(a => ({ ...a, enabled: !!a.enabled })),
         ...providers.map(p => ({