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>

lib/db.ts

@@ -0,0 +1,37 @@
+import Database from 'better-sqlite3';
+import path from 'path';
+
+const DB_PATH = path.join(process.cwd(), 'data', 'bodenfeuchte.db');
+
+let db: Database.Database;
+
+export function getDb(): Database.Database {
+  if (!db) {
+    db = new Database(DB_PATH);
+    db.exec(`
+      CREATE TABLE IF NOT EXISTS measurements (
+        id        INTEGER PRIMARY KEY AUTOINCREMENT,
+        timestamp INTEGER NOT NULL,
+        soil_moisture REAL NOT NULL
+      );
+      CREATE INDEX IF NOT EXISTS idx_timestamp ON measurements(timestamp);
+    `);
+  }
+  return db;
+}
+
+export function insertMeasurement(soilMoisture: number): void {
+  const stmt = getDb().prepare(
+    'INSERT INTO measurements (timestamp, soil_moisture) VALUES (?, ?)'
+  );
+  stmt.run(Date.now(), soilMoisture);
+}
+
+export function getLast6Hours(): { timestamp: number; soil_moisture: number }[] {
+  const since = Date.now() - 6 * 60 * 60 * 1000;
+  return getDb()
+    .prepare(
+      'SELECT timestamp, soil_moisture FROM measurements WHERE timestamp >= ? ORDER BY timestamp ASC'
+    )
+    .all(since) as { timestamp: number; soil_moisture: number }[];
+}

lib/mqtt-listener.ts

@@ -0,0 +1,35 @@
+import mqtt from 'mqtt';
+import { insertMeasurement } from './db';
+
+const TOPIC = 'zigbee2mqtt/Bodenfeuchte_1';
+
+export function startMqttListener(): void {
+  const client = mqtt.connect({
+    host: process.env.MQTT_BROKER ?? 'nuccy',
+    port: Number(process.env.MQTT_PORT ?? 1882),
+    username: process.env.MQTT_USER ?? 'rxf',
+    password: process.env.MQTT_PASSWORD ?? '',
+  });
+
+  client.on('connect', () => {
+    console.log('[MQTT] Connected, subscribing to', TOPIC);
+    client.subscribe(TOPIC);
+  });
+
+  client.on('message', (_topic, payload) => {
+    try {
+      const data = JSON.parse(payload.toString());
+      const value = data?.soil_moisture;
+      if (typeof value === 'number') {
+        insertMeasurement(value);
+        console.log('[MQTT] Stored soil_moisture:', value);
+      }
+    } catch {
+      console.error('[MQTT] Failed to parse message');
+    }
+  });
+
+  client.on('error', (err) => {
+    console.error('[MQTT] Error:', err.message);
+  });
+}