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/routes/admin.ts

@@ -200,6 +200,24 @@ router.put('/bag-tracking', (req: Request, res: Response) => {
   res.json(result);
 });
 
+// ── Collab Features ───────────────────────────────────────────────────────
+
+router.get('/collab-features', (_req: Request, res: Response) => {
+  res.json(svc.getCollabFeatures());
+});
+
+router.put('/collab-features', (req: Request, res: Response) => {
+  const result = svc.updateCollabFeatures(req.body);
+  const authReq = req as AuthRequest;
+  writeAudit({
+    userId: authReq.user.id,
+    action: 'admin.collab_features',
+    ip: getClientIp(req),
+    details: result,
+  });
+  res.json(result);
+});
+
 // ── Packing Templates ──────────────────────────────────────────────────────
 
 router.get('/packing-templates', (_req: Request, res: Response) => {