v0.5.0: Backup bugfixes + monitoring page with metrics store

- Fix "Helyi mentés" showing "–" after controller restart by synthesizing
  LastBackup from snapshot history and LastDBDump from dump files on disk
- New monitoring page (/monitoring) with system info, metrics charts, and
  container resource overview
- SQLite metrics store (modernc.org/sqlite, pure Go, no CGO) with 60s
  collection interval and 30-day auto-prune
- REST API endpoints: /api/metrics/system, /api/metrics/containers/summary,
  /api/metrics/containers/{name}, /api/metrics/sysinfo
- Chart.js 4.4.7 embedded locally for offline environments
- System info provider reads hostname, OS, kernel, CPU, uptime from /proc
- Docker compose updated with /etc/os-release host mount

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

controller/cmd/controller/main.go

@@ -14,6 +14,7 @@ import (
 	"gitea.dooplex.hu/admin/felhom-controller/internal/api"
 	"gitea.dooplex.hu/admin/felhom-controller/internal/backup"
 	"gitea.dooplex.hu/admin/felhom-controller/internal/config"
+	"gitea.dooplex.hu/admin/felhom-controller/internal/metrics"
 	"gitea.dooplex.hu/admin/felhom-controller/internal/monitor"
 	"gitea.dooplex.hu/admin/felhom-controller/internal/scheduler"
 	"gitea.dooplex.hu/admin/felhom-controller/internal/stacks"
@@ -74,6 +75,23 @@ func main() {
 	cpuCollector.Start(ctx)
 	defer cpuCollector.Stop()
 
+	// --- Initialize metrics store + collector ---
+	metricsDBPath := "/opt/docker/felhom-controller/data/metrics.db"
+	metricsStore, err := metrics.NewMetricsStore(metricsDBPath, logger)
+	if err != nil {
+		logger.Printf("[WARN] Failed to initialize metrics store: %v — monitoring disabled", err)
+	} else {
+		logger.Printf("[INFO] Metrics store opened at %s", metricsDBPath)
+	}
+
+	if metricsStore != nil {
+		defer metricsStore.Close()
+		metricsCollector := metrics.NewMetricsCollector(metricsStore, cpuCollector, cfg.Paths.HDDPath, logger)
+		metricsCollector.Start(ctx)
+		defer metricsCollector.Stop()
+		logger.Println("[INFO] Metrics collector started (60s interval)")
+	}
+
 	// --- Initialize health pinger ---
 	pinger := monitor.NewPinger(&cfg.Monitoring, logger)
 
@@ -135,6 +153,18 @@ func main() {
 		})
 	}
 
+	// Metrics prune — daily at 04:00
+	if metricsStore != nil {
+		sched.Daily("metrics-prune", "04:00", func(ctx context.Context) error {
+			deleted, err := metricsStore.Prune(30 * 24 * time.Hour)
+			if err != nil {
+				return err
+			}
+			logger.Printf("[INFO] Pruned %d old metric rows", deleted)
+			return nil
+		})
+	}
+
 	sched.Start(ctx)
 	defer sched.Stop()
 
@@ -148,7 +178,7 @@ func main() {
 	}
 
 	// --- Initialize API router ---
-	apiRouter := api.NewRouter(cfg, stackMgr, syncer, cpuCollector, backupMgr, logger)
+	apiRouter := api.NewRouter(cfg, stackMgr, syncer, cpuCollector, backupMgr, metricsStore, logger)
 
 	// --- Initialize web server ---
 	webServer := web.NewServer(cfg, stackMgr, cpuCollector, backupMgr, sched, logger, Version)