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/internal/web/server.go

@@ -64,6 +64,8 @@ func (s *Server) ServeHTTP(w http.ResponseWriter, r *http.Request) {
 		s.stacksHandler(w, r)
 	case path == "/backups":
 		s.backupsHandler(w, r)
+	case path == "/monitoring":
+		s.monitoringHandler(w, r)
 	case strings.HasPrefix(path, "/stacks/") && strings.HasSuffix(path, "/logs"):
 		name := strings.TrimPrefix(path, "/stacks/")
 		name = strings.TrimSuffix(name, "/logs")
@@ -74,6 +76,8 @@ func (s *Server) ServeHTTP(w http.ResponseWriter, r *http.Request) {
 		s.deployHandler(w, r, name)
 	case path == "/static/style.css":
 		s.serveCSSHandler(w, r)
+	case path == "/static/chart.min.js":
+		s.serveChartJSHandler(w, r)
 	case path == "/static/felhom-logo.svg":
 		s.serveLogoHandler(w, r)
 	case strings.HasPrefix(path, "/static/assets/"):
@@ -107,6 +111,12 @@ func (s *Server) serveCSSHandler(w http.ResponseWriter, r *http.Request) {
 	w.Write(data)
 }
 
+func (s *Server) serveChartJSHandler(w http.ResponseWriter, r *http.Request) {
+	w.Header().Set("Content-Type", "application/javascript; charset=utf-8")
+	w.Header().Set("Cache-Control", "public, max-age=86400")
+	w.Write(chartJS)
+}
+
 func (s *Server) serveLogoHandler(w http.ResponseWriter, r *http.Request) {
 	w.Header().Set("Content-Type", "image/svg+xml")
 	w.Header().Set("Cache-Control", "public, max-age=86400")