Add database backups and two-digit disc numbers

Disc numbers: the organizer writes two-digit disc numbers by default
(Disc 01, 01-04 Title, {disc}), with an option for the plain style
(Disc 2, 2-04). Migration 8 adds the per-pair setting.

Backups (Settings -> Backups), similar to Sonarr:
- A backup is a zip with a consistent snapshot of the database (VACUUM
  INTO, safe while running) and backup.json. Configurable folder,
  schedule (off/1/3/7/14 days) and retention for scheduled backups;
  manual backups are kept until deleted. List, download, delete.
- Restore from a listed backup or an uploaded zip: validated first
  (integrity check, playlink tables, not a newer schema), staged next to
  the live database, then the server restarts; at startup the staged
  database is swapped in and the previous one kept as
  playlink.db.pre-restore-<time>. Refused while a job runs. Backup names
  are validated, so downloads/deletes cannot reach other files.
- Optional backup before every action in live mode: once per action the
  user starts (link, promote, bulk, build/remove, tag edit, folder
  renames, undo, purge) and before scans auto-link or auto-organize,
  never per file and never in dry run. If the backup fails the action
  does not run. The newest 10 action backups are kept.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

internal/engine/organize.go

@@ -76,6 +76,13 @@ func normalizeOrganize(p *store.Pair) error {
 	default:
 		return errors.New("multi-disc style must be prefix, folder or none")
 	}
+	switch p.OrganizeDiscDigits {
+	case 0:
+		p.OrganizeDiscDigits = 2
+	case 1, 2:
+	default:
+		return errors.New("disc numbers must use 1 or 2 digits")
+	}
 	switch p.AutoOrganize {
 	case "":
 		p.AutoOrganize = "off"
@@ -130,7 +137,11 @@ func leadingNumber(s string) int {
 
 // renderName builds the organized path for a file from its tags. It returns
 // the missing tag when a required one is empty.
-func renderName(tpl, multiDisc, ext string, f map[string]string) (string, string) {
+func renderName(tpl, multiDisc string, discDigits int, ext string, f map[string]string) (string, string) {
+	if discDigits < 1 {
+		discDigits = 2
+	}
+	discStr := func(d int) string { return fmt.Sprintf("%0*d", discDigits, d) }
 	artist := f[tags.AlbumArtist]
 	if strings.TrimSpace(artist) == "" {
 		artist = f[tags.Artist]
@@ -147,7 +158,7 @@ func renderName(tpl, multiDisc, ext string, f map[string]string) (string, string
 		}
 		trackStr = fmt.Sprintf("%0*d", width, track)
 		if multi && multiDisc == "prefix" && disc > 0 {
-			trackStr = fmt.Sprintf("%d-%s", disc, trackStr)
+			trackStr = discStr(disc) + "-" + trackStr
 		}
 	}
 	year := ""
@@ -156,7 +167,7 @@ func renderName(tpl, multiDisc, ext string, f map[string]string) (string, string
 	}
 	values := map[string]string{
 		"artist": artist, "track_artist": f[tags.Artist], "album": f[tags.Album], "track": trackStr,
-		"title": f[tags.Title], "disc": strconv.Itoa(disc), "year": year, "genre": f[tags.Genre],
+		"title": f[tags.Title], "disc": discStr(disc), "year": year, "genre": f[tags.Genre],
 	}
 	if disc == 0 {
 		values["disc"] = ""
@@ -188,7 +199,7 @@ func renderName(tpl, multiDisc, ext string, f map[string]string) (string, string
 	}
 	if multi && multiDisc == "folder" && disc > 0 {
 		last := len(parts) - 1
-		parts = append(parts[:last], fmt.Sprintf("Disc %d", disc), parts[last])
+		parts = append(parts[:last], "Disc "+discStr(disc), parts[last])
 	}
 	return filepath.Join(parts...) + strings.ToLower(ext), ""
 }
@@ -293,7 +304,7 @@ func (e *Engine) planOrganize(ctx context.Context, j *Job, l *libs, sides []stri
 				item.Reason = "file type without editable tags"
 			} else if fields, err := e.tagCache.get(ctx, e.tagTools, filepath.Join(root.Path, rel), in); err != nil {
 				item.Reason = "tags could not be read"
-			} else if to, missing := renderName(l.pair.OrganizeTemplate, l.pair.OrganizeMultiDisc, filepath.Ext(rel), fields); missing != "" {
+			} else if to, missing := renderName(l.pair.OrganizeTemplate, l.pair.OrganizeMultiDisc, l.pair.OrganizeDiscDigits, filepath.Ext(rel), fields); missing != "" {
 				item.Reason = "missing " + missing + " tag"
 			} else if to == rel {
 				plan.Conforming++
@@ -616,6 +627,9 @@ func (e *Engine) autoOrganize(ctx context.Context, j *Job, l *libs) error {
 	if len(moves) == 0 {
 		return nil
 	}
+	if err := e.BeforeAction(ctx, "auto-organize"); err != nil {
+		return err
+	}
 	e.log.Info("auto-organizing", "pair", l.pair.Name, "files", len(moves))
 	return e.applyOrganize(ctx, j, l, moves, "auto-organize")
 }