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/store/models.go

@@ -150,8 +150,9 @@ type Pair struct {
 	ApproxMatching      bool      `json:"approx_matching"`
 	ApproxThreshold     int       `json:"approx_threshold"` // percent
 	OrganizeTemplate    string    `json:"organize_template"`
-	OrganizeMultiDisc   string    `json:"organize_multidisc"` // prefix, folder or none
-	AutoOrganize        string    `json:"auto_organize"`      // off, slave, master or both
+	OrganizeMultiDisc   string    `json:"organize_multidisc"`   // prefix, folder or none
+	AutoOrganize        string    `json:"auto_organize"`        // off, slave, master or both
+	OrganizeDiscDigits  int       `json:"organize_disc_digits"` // 2: Disc 01, 1: Disc 1
 	LastScanAt          *int64    `json:"last_scan_at"`
 	LastScanError       string    `json:"last_scan_error"`
 	LastScanWarnings    []Warning `json:"last_scan_warnings"`
@@ -160,7 +161,7 @@ type Pair struct {
 
 const pairCols = `id, name, master_root, slave_root, quarantine_dir, extensions, auto_link_identical,
 	scan_interval_minutes, retention_days, settle_minutes, approx_matching, approx_threshold, organize_template,
-	organize_multidisc, auto_organize, last_scan_at, last_scan_error,
+	organize_multidisc, auto_organize, organize_disc_digits, last_scan_at, last_scan_error,
 	last_scan_warnings, created_at`
 
 type scanner interface{ Scan(...any) error }
@@ -171,7 +172,7 @@ func scanPair(r scanner) (Pair, error) {
 	var last sql.NullInt64
 	err := r.Scan(&p.ID, &p.Name, &p.MasterRoot, &p.SlaveRoot, &p.QuarantineDir, &exts, &p.AutoLinkIdentical,
 		&p.ScanIntervalMinutes, &p.RetentionDays, &p.SettleMinutes, &p.ApproxMatching, &p.ApproxThreshold, &p.OrganizeTemplate,
-		&p.OrganizeMultiDisc, &p.AutoOrganize, &last, &p.LastScanError,
+		&p.OrganizeMultiDisc, &p.AutoOrganize, &p.OrganizeDiscDigits, &last, &p.LastScanError,
 		&warns, &p.CreatedAt)
 	if err != nil {
 		return p, err
@@ -214,11 +215,11 @@ func (s *Store) SavePair(ctx context.Context, p *Pair) error {
 	if p.ID == 0 {
 		res, err := s.DB.ExecContext(ctx, `INSERT INTO pairs (name, master_root, slave_root, quarantine_dir, extensions,
 			auto_link_identical, scan_interval_minutes, retention_days, settle_minutes, approx_matching, approx_threshold,
-			organize_template, organize_multidisc, auto_organize, created_at)
-			VALUES (?, ?, ?, ?, ?, ?, ?, ?, ?, ?, ?, ?, ?, ?, ?)`,
+			organize_template, organize_multidisc, auto_organize, organize_disc_digits, created_at)
+			VALUES (?, ?, ?, ?, ?, ?, ?, ?, ?, ?, ?, ?, ?, ?, ?, ?)`,
 			p.Name, p.MasterRoot, p.SlaveRoot, p.QuarantineDir, exts, p.AutoLinkIdentical,
 			p.ScanIntervalMinutes, p.RetentionDays, p.SettleMinutes, p.ApproxMatching, p.ApproxThreshold,
-			p.OrganizeTemplate, p.OrganizeMultiDisc, p.AutoOrganize, now())
+			p.OrganizeTemplate, p.OrganizeMultiDisc, p.AutoOrganize, p.OrganizeDiscDigits, now())
 		if err != nil {
 			return err
 		}
@@ -227,10 +228,11 @@ func (s *Store) SavePair(ctx context.Context, p *Pair) error {
 	}
 	_, err := s.DB.ExecContext(ctx, `UPDATE pairs SET name = ?, master_root = ?, slave_root = ?, quarantine_dir = ?,
 		extensions = ?, auto_link_identical = ?, scan_interval_minutes = ?, retention_days = ?, settle_minutes = ?,
-		approx_matching = ?, approx_threshold = ?, organize_template = ?, organize_multidisc = ?, auto_organize = ? WHERE id = ?`,
+		approx_matching = ?, approx_threshold = ?, organize_template = ?, organize_multidisc = ?, auto_organize = ?,
+		organize_disc_digits = ? WHERE id = ?`,
 		p.Name, p.MasterRoot, p.SlaveRoot, p.QuarantineDir, exts, p.AutoLinkIdentical,
 		p.ScanIntervalMinutes, p.RetentionDays, p.SettleMinutes, p.ApproxMatching, p.ApproxThreshold,
-		p.OrganizeTemplate, p.OrganizeMultiDisc, p.AutoOrganize, p.ID)
+		p.OrganizeTemplate, p.OrganizeMultiDisc, p.AutoOrganize, p.OrganizeDiscDigits, p.ID)
 	return err
 }
 

internal/store/store.go

@@ -126,8 +126,14 @@ var migrations = []string{
 	`ALTER TABLE pairs ADD COLUMN organize_template TEXT NOT NULL DEFAULT '';
 	ALTER TABLE pairs ADD COLUMN organize_multidisc TEXT NOT NULL DEFAULT 'prefix';
 	ALTER TABLE pairs ADD COLUMN auto_organize TEXT NOT NULL DEFAULT 'off';`,
+
+	// 8: zero-padded disc numbers (Disc 01) by default.
+	`ALTER TABLE pairs ADD COLUMN organize_disc_digits INTEGER NOT NULL DEFAULT 2;`,
 }
 
+// SchemaVersion is the newest database schema this build knows.
+func SchemaVersion() int { return len(migrations) }
+
 // Open opens (and migrates) the database in dataDir.
 func Open(dataDir string) (*Store, error) {
 	dsn := "file:" + filepath.Join(dataDir, "playlink.db") +