Implement Bodenfeuchte app: MQTT listener, SQLite storage, chart UI, Docker

- Custom Next.js server starts MQTT listener on boot
- Subscribes to zigbee2mqtt/Bodenfeuchte_1, stores soil_moisture in SQLite
- API route /api/data returns last 6 hours of measurements
- Frontend shows current value + Recharts line chart, auto-refresh every 60s
- Dockerfile + docker-compose with persistent volume for SQLite DB

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

server.ts

@@ -0,0 +1,19 @@
+import { createServer } from 'http';
+import { parse } from 'url';
+import next from 'next';
+import { startMqttListener } from './lib/mqtt-listener';
+
+const dev = process.env.NODE_ENV !== 'production';
+const app = next({ dev });
+const handle = app.getRequestHandler();
+
+app.prepare().then(() => {
+  startMqttListener();
+
+  createServer((req, res) => {
+    const parsedUrl = parse(req.url ?? '/', true);
+    handle(req, res, parsedUrl);
+  }).listen(3000, () => {
+    console.log('> Ready on http://localhost:3000');
+  });
+});