fix: add topic selection checkbox that auto-creates datapoints

When a user checks a topic checkbox, a datapoint is automatically
created and the broker subscribes to that topic for live updates.

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

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

@@ -5,6 +5,9 @@ import {
   startDiscovery,
   addManualTopic,
 } from '../../modules/mqtt/topic-discovery';
+import { createDatapointFromMqtt, getDatapointByTopicId } from '../../modules/datapoints/datapoint-manager';
+import { getConnection } from './../../modules/mqtt/broker-manager';
+import { getDb } from '../../db/index';
 
 const router = Router({ mergeParams: true });
 
@@ -21,8 +24,23 @@ router.get('/', (req, res): void => {
 // PUT /api/mqtt/brokers/:brokerId/topics/:id
 router.put('/:id', (req, res): void => {
   try {
-    const topic = updateTopic(parseInt(req.params.id), req.body);
-    if (!topic) { res.status(404).json({ error: 'Topic not found' }); return; }
+    const topicId = parseInt(req.params.id);
+    const topicRow = getDb().prepare('SELECT * FROM mqtt_topics WHERE id = ?').get(topicId) as any;
+    if (!topicRow) { res.status(404).json({ error: 'Topic not found' }); return; }
+
+    const topic = updateTopic(topicId, req.body);
+
+    // If selecting a topic, auto-create a datapoint
+    if (req.body.selected === 1 || req.body.selected === true) {
+      const existing = getDatapointByTopicId(topicId);
+      if (!existing) {
+        createDatapointFromMqtt(topicRow.broker_id, topicId, topicRow.topic);
+      }
+      // Subscribe to the topic on the broker connection
+      const client = getConnection(topicRow.broker_id);
+      if (client?.connected) client.subscribe(topicRow.topic);
+    }
+
     res.json(topic);
   } catch (err) {
     res.status(500).json({ error: (err as Error).message });