perf: server-side search + pagination for topics (30 per page)

Loads only 30 topics at a time with server-side search instead
of fetching all 6000+ topics. Debounced search input, pagination,
selected-only filter. Much faster for large Victron brokers.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

display/middleware/src/api/routes/mqtt-topics.ts

@@ -11,11 +11,15 @@ import { getDb } from '../../db/index';
 
 const router = Router({ mergeParams: true });
 
-// GET /api/mqtt/brokers/:brokerId/topics
+// GET /api/mqtt/brokers/:brokerId/topics?search=grid&selected=1&limit=50&offset=0
 router.get('/', (req, res): void => {
   try {
     const brokerId = parseInt(req.params.brokerId);
-    res.json(getTopicsForBroker(brokerId));
+    const search = req.query.search as string | undefined;
+    const selectedOnly = req.query.selected === '1';
+    const limit = parseInt(req.query.limit as string) || 50;
+    const offset = parseInt(req.query.offset as string) || 0;
+    res.json(getTopicsForBroker(brokerId, { search, selectedOnly, limit, offset }));
   } catch (err) {
     res.status(500).json({ error: (err as Error).message });
   }