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>

docker-compose.yml

@@ -0,0 +1,13 @@
+services:
+  bodenfeuchte:
+    build: .
+    ports:
+      - "3000:3000"
+    volumes:
+      - bodenfeuchte-data:/app/data
+    env_file:
+      - .env
+    restart: unless-stopped
+
+volumes:
+  bodenfeuchte-data: