Phase 2: monitoring warnings, dashboard alerts & notification system

- Monitoring page: "Távoli monitoring" section showing healthcheck ping UUID
  configuration status (configured/not configured) for each of the 5 pings
- Alert manager: persistent dashboard banners on all pages generated from
  health check results, missing pings, and backup status
- Notification system: controller-side notifier sends events to hub relay,
  with cooldown tracking and event-type filtering
- Notification preferences UI: email, event checkboxes, cooldown settings
  on the settings page with test email functionality
- Settings refactored: shared settingsData() helper, NotificationPrefs
  struct with getter/setter and defaults

New files:
- controller/internal/web/alerts.go (AlertManager)
- controller/internal/notify/notifier.go (hub notification client)

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

controller/internal/web/server.go

@@ -12,6 +12,7 @@ import (
 
 	"gitea.dooplex.hu/admin/felhom-controller/internal/backup"
 	"gitea.dooplex.hu/admin/felhom-controller/internal/config"
+	"gitea.dooplex.hu/admin/felhom-controller/internal/notify"
 	"gitea.dooplex.hu/admin/felhom-controller/internal/scheduler"
 	"gitea.dooplex.hu/admin/felhom-controller/internal/settings"
 	"gitea.dooplex.hu/admin/felhom-controller/internal/stacks"
@@ -25,6 +26,8 @@ type Server struct {
 	backupMgr    *backup.Manager
 	scheduler    *scheduler.Scheduler
 	settings     *settings.Settings
+	alertManager *AlertManager
+	notifier     *notify.Notifier
 	logger       *log.Logger
 	version      string
 	tmpl         *template.Template
@@ -34,7 +37,7 @@ type Server struct {
 	done       chan struct{}
 }
 
-func NewServer(cfg *config.Config, stackMgr *stacks.Manager, cpuCollector *system.CPUCollector, backupMgr *backup.Manager, sched *scheduler.Scheduler, sett *settings.Settings, logger *log.Logger, version string) *Server {
+func NewServer(cfg *config.Config, stackMgr *stacks.Manager, cpuCollector *system.CPUCollector, backupMgr *backup.Manager, sched *scheduler.Scheduler, sett *settings.Settings, alertMgr *AlertManager, notif *notify.Notifier, logger *log.Logger, version string) *Server {
 	s := &Server{
 		cfg:          cfg,
 		stackMgr:     stackMgr,
@@ -42,6 +45,8 @@ func NewServer(cfg *config.Config, stackMgr *stacks.Manager, cpuCollector *syste
 		backupMgr:    backupMgr,
 		scheduler:    sched,
 		settings:     sett,
+		alertManager: alertMgr,
+		notifier:     notif,
 		logger:       logger,
 		version:      version,
 		sessions:     make(map[string]*session),
@@ -85,6 +90,10 @@ func (s *Server) ServeHTTP(w http.ResponseWriter, r *http.Request) {
 		s.settingsHandler(w, r)
 	case path == "/settings/password" && r.Method == http.MethodPost:
 		s.settingsPasswordHandler(w, r)
+	case path == "/settings/notifications" && r.Method == http.MethodPost:
+		s.settingsNotificationsHandler(w, r)
+	case path == "/settings/notifications/test" && r.Method == http.MethodPost:
+		s.settingsNotificationsTestHandler(w, r)
 	case strings.HasPrefix(path, "/stacks/") && strings.HasSuffix(path, "/logs"):
 		name := strings.TrimPrefix(path, "/stacks/")
 		name = strings.TrimSuffix(name, "/logs")