feat: Hub monitoring takeover — event push system + config cleanup (v0.21.0)

Replace external Healthchecks.io with Hub-native event system. Controller
now pushes structured events via POST /api/v1/event with typed detail
structs. Hub handles dead man's switch, notification dispatch, and cooldowns.

Phase 5: PushEvent() core method, 21 event types, expanded notification
settings (11 toggles), Hub connection monitoring on dashboard, alerts.
Phase 6: Deprecation log for ping UUIDs, pinger kept for transition.

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

controller/internal/web/server.go

@@ -9,6 +9,7 @@ import (
 	"path/filepath"
 	"strings"
 	"sync"
+	"time"
 
 	"gitea.dooplex.hu/admin/felhom-controller/internal/backup"
 	"gitea.dooplex.hu/admin/felhom-controller/internal/config"
@@ -57,6 +58,9 @@ type Server struct {
 
 	// Storage watchdog (set after construction to break init ordering)
 	storageWatchdog *monitor.StorageWatchdog
+
+	// Hub push status callback — set via SetHubPushStatus for monitoring page
+	hubPushStatusFn func() HubPushStatusData
 }
 
 func NewServer(cfg *config.Config, stackMgr *stacks.Manager, cpuCollector *system.CPUCollector, backupMgr *backup.Manager, crossDrive *backup.CrossDriveRunner, sched *scheduler.Scheduler, sett *settings.Settings, alertMgr *AlertManager, notif *notify.Notifier, updater *selfupdate.Updater, logger *log.Logger, version string) *Server {
@@ -117,6 +121,19 @@ func (s *Server) SetDriveMigrator(dm *storage.DriveMigrator) {
 	s.driveMigrator = dm
 }
 
+// HubPushStatusData holds hub push status for the monitoring page.
+type HubPushStatusData struct {
+	LastAttempt time.Time
+	LastSuccess time.Time
+	LastError   string
+	Consecutive int
+}
+
+// SetHubPushStatus sets the hub push status callback for the monitoring page.
+func (s *Server) SetHubPushStatus(fn func() HubPushStatusData) {
+	s.hubPushStatusFn = fn
+}
+
 // InRestoreMode returns true if the server is in DR restore mode.
 func (s *Server) InRestoreMode() bool {
 	s.restoreMu.RLock()