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 });
   }

display/middleware/src/modules/mqtt/topic-discovery.ts

@@ -19,11 +19,32 @@ export interface UpdateTopicData {
   ignored?: number;
 }
 
-export function getTopicsForBroker(brokerId: number): MqttTopic[] {
+export function getTopicsForBroker(brokerId: number, opts?: { search?: string; selectedOnly?: boolean; limit?: number; offset?: number }): { topics: MqttTopic[]; total: number } {
   const db = getDb();
-  return db
-    .prepare('SELECT * FROM mqtt_topics WHERE broker_id = ? ORDER BY id ASC')
-    .all(brokerId) as MqttTopic[];
+  const conditions = ['broker_id = ?'];
+  const params: any[] = [brokerId];
+
+  if (opts?.search) {
+    conditions.push('topic LIKE ?');
+    params.push(`%${opts.search}%`);
+  }
+  if (opts?.selectedOnly) {
+    conditions.push('selected = 1');
+  }
+  conditions.push('ignored = 0');
+
+  const where = conditions.join(' AND ');
+  const total = (db.prepare(`SELECT count(*) as c FROM mqtt_topics WHERE ${where}`).get(...params) as any).c;
+
+  const limit = opts?.limit || 50;
+  const offset = opts?.offset || 0;
+  params.push(limit, offset);
+
+  const topics = db
+    .prepare(`SELECT * FROM mqtt_topics WHERE ${where} ORDER BY selected DESC, last_payload IS NOT NULL DESC, topic ASC LIMIT ? OFFSET ?`)
+    .all(...params) as MqttTopic[];
+
+  return { topics, total };
 }
 
 export function updateTopic(id: number, data: UpdateTopicData): MqttTopic | undefined {