fix(photos): paginated search with infinite scroll (#613)

Replace bulk-loading all Immich photos (up to 20k) with paginated
search: 50 photos per page, automatic infinite scroll via
IntersectionObserver. Prevents server blocking on large libraries.

- Backend: searchPhotos accepts page/size params, returns hasMore
- Frontend: loads 50 at a time, appends on scroll
- AbortController cancels in-flight requests on tab switch

server/src/routes/memories/immich.ts

@@ -60,10 +60,10 @@ router.get('/browse', authenticate, async (req: Request, res: Response) => {
 
 router.post('/search', authenticate, async (req: Request, res: Response) => {
   const authReq = req as AuthRequest;
-  const { from, to } = req.body;
-  const result = await searchPhotos(authReq.user.id, from, to);
+  const { from, to, page, size } = req.body;
+  const result = await searchPhotos(authReq.user.id, from, to, Number(page) || 1, Math.min(Number(size) || 50, 200));
   if (result.error) return res.status(result.status!).json({ error: result.error });
-  res.json({ assets: result.assets });
+  res.json({ assets: result.assets, hasMore: result.hasMore });
 });
 
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