Notifications, and automatic cleanup of empty folders

Settings → Notifications sends a message to Discord, Pushover, ntfy,
Gotify or a JSON webhook when a scan finds songs that newly need
review, when auto-link replaced identical files, and when an automatic
cleanup ran. Each event can be turned off and each service tested; an
optional Playlink address adds a link back to the right page.

A new per-pair option removes empty slave folders after each scan. Only
folders with no file at all inside are removed (into the quarantine,
recorded in History); folders holding any file wait in Cleanup, folders
changed within the settle time are skipped, and dry run removes nothing.

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

internal/store/models.go

@@ -144,6 +144,7 @@ type Pair struct {
 	QuarantineDir       string    `json:"quarantine_dir"`
 	Extensions          []string  `json:"extensions"`
 	AutoLinkIdentical   bool      `json:"auto_link_identical"`
+	AutoCleanupEmpty    bool      `json:"auto_cleanup_empty"` // remove empty slave folders after each scan
 	ScanIntervalMinutes int       `json:"scan_interval_minutes"`
 	RetentionDays       int       `json:"retention_days"`
 	SettleMinutes       int       `json:"settle_minutes"`
@@ -155,7 +156,7 @@ type Pair struct {
 	CreatedAt           int64     `json:"created_at"`
 }
 
-const pairCols = `id, name, master_root, slave_root, quarantine_dir, extensions, auto_link_identical,
+const pairCols = `id, name, master_root, slave_root, quarantine_dir, extensions, auto_link_identical, auto_cleanup_empty,
 	scan_interval_minutes, retention_days, settle_minutes, approx_matching, approx_threshold, last_scan_at, last_scan_error,
 	last_scan_warnings, created_at`
 
@@ -165,7 +166,7 @@ func scanPair(r scanner) (Pair, error) {
 	var p Pair
 	var exts, warns string
 	var last sql.NullInt64
-	err := r.Scan(&p.ID, &p.Name, &p.MasterRoot, &p.SlaveRoot, &p.QuarantineDir, &exts, &p.AutoLinkIdentical,
+	err := r.Scan(&p.ID, &p.Name, &p.MasterRoot, &p.SlaveRoot, &p.QuarantineDir, &exts, &p.AutoLinkIdentical, &p.AutoCleanupEmpty,
 		&p.ScanIntervalMinutes, &p.RetentionDays, &p.SettleMinutes, &p.ApproxMatching, &p.ApproxThreshold, &last, &p.LastScanError,
 		&warns, &p.CreatedAt)
 	if err != nil {
@@ -208,9 +209,9 @@ func (s *Store) SavePair(ctx context.Context, p *Pair) error {
 	exts := strings.Join(p.Extensions, ",")
 	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, created_at)
-			VALUES (?, ?, ?, ?, ?, ?, ?, ?, ?, ?, ?, ?)`,
-			p.Name, p.MasterRoot, p.SlaveRoot, p.QuarantineDir, exts, p.AutoLinkIdentical,
+			auto_link_identical, auto_cleanup_empty, scan_interval_minutes, retention_days, settle_minutes, approx_matching, approx_threshold, created_at)
+			VALUES (?, ?, ?, ?, ?, ?, ?, ?, ?, ?, ?, ?, ?)`,
+			p.Name, p.MasterRoot, p.SlaveRoot, p.QuarantineDir, exts, p.AutoLinkIdentical, p.AutoCleanupEmpty,
 			p.ScanIntervalMinutes, p.RetentionDays, p.SettleMinutes, p.ApproxMatching, p.ApproxThreshold, now())
 		if err != nil {
 			return err
@@ -219,9 +220,9 @@ func (s *Store) SavePair(ctx context.Context, p *Pair) error {
 		return nil
 	}
 	_, 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 = ?,
+		extensions = ?, auto_link_identical = ?, auto_cleanup_empty = ?, scan_interval_minutes = ?, retention_days = ?, settle_minutes = ?,
 		approx_matching = ?, approx_threshold = ? WHERE id = ?`,
-		p.Name, p.MasterRoot, p.SlaveRoot, p.QuarantineDir, exts, p.AutoLinkIdentical,
+		p.Name, p.MasterRoot, p.SlaveRoot, p.QuarantineDir, exts, p.AutoLinkIdentical, p.AutoCleanupEmpty,
 		p.ScanIntervalMinutes, p.RetentionDays, p.SettleMinutes, p.ApproxMatching, p.ApproxThreshold, p.ID)
 	return err
 }