Add go-e wallbox charger integration

- charger.go: polls go-e /api/status?filter=nrg,eto every 10 s
- db.go: WriteCharger() inserts into charger hypertable
- config.go: ChargerConf with host field
- main.go: polls charger in parallel with inverter and meters
- schema.sql: charger table + charger_10m/1h/daily aggregates + policies

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

main.go

@@ -44,7 +44,7 @@ func main() {
 	defer meters.Close()
 
 	interval := time.Duration(cfg.SampleRate) * time.Second
-	go runPollLoop(ctx, alpha, meters, db, interval)
+	go runPollLoop(ctx, alpha, meters, cfg.Charger.Host, db, interval)
 
 	sig := make(chan os.Signal, 1)
 	signal.Notify(sig, syscall.SIGINT, syscall.SIGTERM)
@@ -52,7 +52,7 @@ func main() {
 	logger.Println("shutting down")
 }
 
-func runPollLoop(ctx context.Context, alpha *AlphaEss, meters *MeterPoller, db *DB, interval time.Duration) {
+func runPollLoop(ctx context.Context, alpha *AlphaEss, meters *MeterPoller, chargerHost string, db *DB, interval time.Duration) {
 	ticker := time.NewTicker(interval)
 	defer ticker.Stop()
 	for {
@@ -60,22 +60,22 @@ func runPollLoop(ctx context.Context, alpha *AlphaEss, meters *MeterPoller, db *
 		case <-ctx.Done():
 			return
 		case <-ticker.C:
-			poll(ctx, alpha, meters, db)
+			poll(ctx, alpha, meters, chargerHost, db)
 		}
 	}
 }
 
-func poll(ctx context.Context, alpha *AlphaEss, meters *MeterPoller, db *DB) {
+func poll(ctx context.Context, alpha *AlphaEss, meters *MeterPoller, chargerHost string, db *DB) {
 	t := time.Now()
 
-	// Poll AlphaEss and all SDM630 meters in parallel.
 	var (
-		inverterData *InverterData
-		meterData    []MeterReading
-		wg           sync.WaitGroup
+		inverterData  *InverterData
+		meterData     []MeterReading
+		chargerData   *ChargerReading
+		wg            sync.WaitGroup
 	)
 
-	wg.Add(2)
+	wg.Add(3)
 	go func() {
 		defer wg.Done()
 		d, err := alpha.Poll()
@@ -89,9 +89,21 @@ func poll(ctx context.Context, alpha *AlphaEss, meters *MeterPoller, db *DB) {
 		defer wg.Done()
 		meterData = meters.PollAll()
 	}()
+	go func() {
+		defer wg.Done()
+		if chargerHost == "" {
+			return
+		}
+		r, err := PollCharger(chargerHost)
+		if err != nil {
+			logger.Printf("charger: %v", err)
+			return
+		}
+		r.Time = t
+		chargerData = &r
+	}()
 	wg.Wait()
 
-	// Write everything with the same timestamp t.
 	if inverterData != nil {
 		if err := db.WriteInverter(ctx, t, inverterData); err != nil {
 			logger.Printf("write inverter: %v", err)
@@ -102,4 +114,9 @@ func poll(ctx context.Context, alpha *AlphaEss, meters *MeterPoller, db *DB) {
 			logger.Printf("write meter %s: %v", r.Device, err)
 		}
 	}
+	if chargerData != nil {
+		if err := db.WriteCharger(ctx, *chargerData); err != nil {
+			logger.Printf("write charger: %v", err)
+		}
+	}
 }