controller v0.69.0: remove dead infra-backup stubs + unused restic-password report field

Controller half of Phase-1 Infra Backup retirement (hub v0.12.0;
SPIKE-infra-backup-2026-06-15). Pure dead-code removal, no behaviour change.

- Remove Pusher.PushInfraBackup (caller-less; hub endpoint gone).
- Remove Notifier.NotifyBackupCompleted / backup_completed event (caller-less
  since slice 8C; hub deadline check now reads agent host-report PBS snapshots).
- Remove report.BackupReport.ResticPassword — builder never sets it post-8C
  (confirmed in source + live), but it historically leaked the restic password
  into the hub's plaintext reports store.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

controller/internal/notify/notifier.go

@@ -276,10 +276,10 @@ func (n *Notifier) NotifyBackupFailed(message, errMsg string) {
 	n.PushEvent("backup_failed", "error", message, BackupDetails{Error: errMsg})
 }
 
-// NotifyBackupCompleted sends a backup success event.
-func (n *Notifier) NotifyBackupCompleted(details BackupDetails) {
-	n.PushEvent("backup_completed", "info", "Biztonsági mentés elkészült", details)
-}
+// (NotifyBackupCompleted removed 2026-06-16 — the backup_completed event had no callers
+// since slice 8C moved whole-guest backup to the agent. The hub's backup-deadline check
+// now reads the agent host-report's PBS snapshots instead of this event. DB-dump events
+// below are still emitted and consumed.)
 
 // NotifyDBDumpFailed sends a DB dump failure event.
 func (n *Notifier) NotifyDBDumpFailed(message, errMsg string) {