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/backup/restic.go

@@ -216,6 +216,34 @@ func (r *ResticManager) Check() error {
 	return nil
 }
 
+// ListSnapshots returns all snapshots, newest first, limited to N entries.
+func (r *ResticManager) ListSnapshots(limit int) ([]SnapshotInfo, error) {
+	ctx, cancel := context.WithTimeout(context.Background(), 2*time.Minute)
+	defer cancel()
+
+	cmd := r.command(ctx, "snapshots", "--json")
+	out, err := cmd.Output()
+	if err != nil {
+		return nil, fmt.Errorf("restic snapshots failed: %v", err)
+	}
+
+	var snapshots []SnapshotInfo
+	if err := json.Unmarshal(out, &snapshots); err != nil {
+		return nil, fmt.Errorf("parsing snapshot JSON: %v", err)
+	}
+
+	// Reverse for newest first
+	for i, j := 0, len(snapshots)-1; i < j; i, j = i+1, j-1 {
+		snapshots[i], snapshots[j] = snapshots[j], snapshots[i]
+	}
+
+	if limit > 0 && len(snapshots) > limit {
+		snapshots = snapshots[:limit]
+	}
+
+	return snapshots, nil
+}
+
 // LatestSnapshot returns the most recent snapshot info.
 func (r *ResticManager) LatestSnapshot() (*SnapshotInfo, error) {
 	ctx, cancel := context.WithTimeout(context.Background(), 1*time.Minute)