Add per-app MQTT Broker (Plant) integration slug

Lets plant have its own dedicated MQTT credentials instead of sharing
the single central mqtt integration with utilities/hvac, so its
dynsec client can be scoped to plant/# without touching other apps'
access. Generalizes the test-connection dispatch to match any
mqtt_* slug, not just the literal 'mqtt' one.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>

src/integrations/schema.js

@@ -52,6 +52,11 @@ export const INTEGRATIONS = {
     configFields: ['host', 'port'],
     secretFields: ['username', 'password'],
   },
+  mqtt_plant: {
+    name: 'MQTT Broker (Plant)',
+    configFields: ['host', 'port'],
+    secretFields: ['username', 'password'],
+  },
 }
 
 export const MASKED = '••••••••'

src/routes/integrations.js

@@ -141,7 +141,7 @@ export async function integrationRoutes(app) {
         if (res.status === 401) throw new Error('Invalid Nextcloud credentials')
         if (!res.ok) throw new Error(`Nextcloud returned ${res.status}`)
       }
-      else if (req.params.slug === 'mqtt') {
+      else if (req.params.slug === 'mqtt' || req.params.slug.startsWith('mqtt_')) {
         if (!creds.host || !creds.username || !creds.password) throw new Error('MQTT host, username and password are required')
         const mqtt = await import('mqtt')
         await new Promise((resolve, reject) => {