v0.4.5: Add dedicated Backup page (Biztonsági mentés)

New /backups page with full backup system visibility:
- Status overview cards (local/remote backup, DB count, repo size)
- Schedule section with next-run times and retention policy
- Database table with type, size, validation (table count), status
- Snapshot history table with per-snapshot stats
- Repository info card with paths, integrity status, remote placeholder
- "Mentés most" button with auto-refresh polling
- Empty state when backup not configured

Backend: SnapshotRecord history (ring buffer), DumpValidation,
ListDumpFiles, ListSnapshots, GetFullStatus, restic check tracking.
Server accepts scheduler for next-run time calculation.

Sidebar nav updated with 3rd item, dashboard backup card title clickable.

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

controller/internal/web/handlers.go

@@ -4,6 +4,7 @@ import (
 	"fmt"
 	"net/http"
 
+	"gitea.dooplex.hu/admin/felhom-controller/internal/scheduler"
 	"gitea.dooplex.hu/admin/felhom-controller/internal/stacks"
 	"gitea.dooplex.hu/admin/felhom-controller/internal/system"
 )
@@ -181,3 +182,18 @@ func (s *Server) appDetailHandler(w http.ResponseWriter, _ *http.Request, slug s
 
 	s.render(w, "app_info", data)
 }
+
+func (s *Server) backupsHandler(w http.ResponseWriter, _ *http.Request) {
+	data := s.baseData("backups", "Biztonsági mentés")
+
+	if s.backupMgr != nil {
+		nextDBDump := scheduler.NextDailyRun(s.cfg.Backup.DBDumpSchedule)
+		nextBackup := scheduler.NextDailyRun(s.cfg.Backup.ResticSchedule)
+		fullStatus := s.backupMgr.GetFullStatus(nextDBDump, nextBackup)
+		data["Backup"] = fullStatus
+	} else {
+		data["Backup"] = nil
+	}
+
+	s.render(w, "backups", data)
+}