Scaffold Phase 1 hvac app — NewBook-driven room TRV heating scheduler

Ports the state machine, retry/backoff, and guest-override detection from
the retired homeassistant-newbook-heating-component, without depending on
Home Assistant. Backend (Fastify/pg) + frontend (React/Vite/TS) following
standard stack conventions; LXC 128 (127 was already taken by utilities).

MHI/Midea/Daikin/boiler drivers and the shared MQTT broker (LXC 104) are
later phases/infra, not included here.

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

backend/src/routes/settings.js

@@ -0,0 +1,25 @@
+import { requireAuth, requireCap } from '../auth.js'
+import { testConnection } from '../lib/newbook.js'
+import { isConnected as mqttConnected } from '../lib/mqtt.js'
+
+// Settings-page-backing endpoints that don't fit the generic config.js key/value
+// store: connection tests and the MQTT broker's live status. The Home Assistant
+// integration itself is configured centrally in the shared `settings` app, not
+// here — this just reports whether it's reachable (via the driver's own no-op
+// behaviour when unconfigured).
+export async function settingsRoutes(app) {
+  app.addHook('preHandler', requireAuth)
+
+  app.post('/api/settings/newbook-test', { preHandler: requireCap('settings') }, async () => {
+    return testConnection()
+  })
+
+  app.get('/api/settings/mqtt-status', { preHandler: requireCap('settings') }, async () => {
+    return {
+      connected: mqttConnected(),
+      note: mqttConnected()
+        ? 'Connected to the shared MQTT broker.'
+        : 'Not connected — the shared MQTT broker (LXC 104) may not be provisioned yet, or hvac-backend has no credentials in settings.',
+    }
+  })
+}