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>

app/api/data/route.ts

@@ -0,0 +1,8 @@
+import { getLast6Hours } from '@/lib/db';
+
+export const dynamic = 'force-dynamic';
+
+export async function GET() {
+  const rows = getLast6Hours();
+  return Response.json(rows);
+}