fix(13-02): auto-resolve phantom playlist tracks after library scan

- Add phantom_file_path column to playlist_tracks (migration 7)
- Store original file_path during RemoveLibrary phantom metadata population
- After each successful scan, UPDATE phantom tracks whose phantom_file_path
  now matches an audio_files row, re-linking them and clearing phantom metadata
- Update schema file, sqlc generated code, and database test for new column

backend/database/database.go

@@ -312,6 +312,16 @@ func runMigrations(
 		}
 	}
 
+	// Migration 7: add phantom_file_path to playlist_tracks
+	// for automatic phantom resolution after library re-scans.
+	if version < 7 {
+		if err := migration7PhantomFilePath(
+			ctx, db, logger,
+		); err != nil {
+			return err
+		}
+	}
+
 	return nil
 }
 
@@ -1030,6 +1040,44 @@ func migration6MultiLibrary(
 	return nil
 }
 
+// migration7PhantomFilePath adds the phantom_file_path column to
+// playlist_tracks so that phantom entries can be automatically
+// re-linked to audio_files after a library scan.
+func migration7PhantomFilePath(
+	ctx context.Context,
+	db *sql.DB,
+	logger *slog.Logger,
+) error {
+	logger.Info(
+		"applying migration 7: phantom_file_path column",
+	)
+
+	// SAFETY: ALTER TABLE ADD COLUMN for new nullable column.
+	if _, err := db.ExecContext(ctx,
+		`ALTER TABLE playlist_tracks
+		 ADD COLUMN phantom_file_path TEXT`,
+	); err != nil {
+		if !isDuplicateColumnErr(err) {
+			return fmt.Errorf(
+				"migration 7: could not add column: %w",
+				err,
+			)
+		}
+	}
+
+	if _, err := db.ExecContext(
+		ctx, "PRAGMA user_version = 7",
+	); err != nil {
+		return fmt.Errorf(
+			"could not set user_version to 7: %w", err,
+		)
+	}
+
+	logger.Info("migration 7 complete")
+
+	return nil
+}
+
 // readLibraryDirFromTOML reads the TOML config file and returns
 // the Library.DirectoryPath value, or "" if not configured.
 func readLibraryDirFromTOML(logger *slog.Logger) string {

backend/database/database_test.go

@@ -91,6 +91,7 @@ func TestMigration6FreshDB(t *testing.T) {
 		"phantom_duration_ms":    false,
 		"phantom_genre":          false,
 		"phantom_cover_art_path": false,
+		"phantom_file_path":      false,
 	}
 
 	audioFileIDNullable := false
@@ -171,7 +172,7 @@ func TestMigration6FreshDB(t *testing.T) {
 		t.Error("track_metadata VIEW does not contain library_id")
 	}
 
-	// Verify user_version >= 6.
+	// Verify user_version >= 7.
 	var version int
 
 	verRows, err := db.QueryContext("PRAGMA user_version")
@@ -193,8 +194,8 @@ func TestMigration6FreshDB(t *testing.T) {
 
 	_ = verRows.Close()
 
-	if version < 6 {
-		t.Errorf("user_version = %d, want >= 6", version)
+	if version < 7 {
+		t.Errorf("user_version = %d, want >= 7", version)
 	}
 
 	// Verify libraries table has only the sentinel row on fresh DB.

backend/database/sql/schemas/playlist_tracks.sql

@@ -9,6 +9,7 @@ CREATE TABLE IF NOT EXISTS playlist_tracks (
     phantom_duration_ms INTEGER,
     phantom_genre TEXT,
     phantom_cover_art_path TEXT,
+    phantom_file_path TEXT,
     FOREIGN KEY(playlist_id) REFERENCES playlists(id) ON DELETE CASCADE,
     FOREIGN KEY(audio_file_id) REFERENCES audio_files(id) ON DELETE SET NULL
 );

backend/database/sql/sqlcgen/models.go

@@ -90,6 +90,7 @@ type PlaylistTrack struct {
 	PhantomDurationMs   sql.NullInt64
 	PhantomGenre        sql.NullString
 	PhantomCoverArtPath sql.NullString
+	PhantomFilePath     sql.NullString
 }
 
 type Queue struct {

backend/database/sql/sqlcgen/playlists.sql.go

@@ -16,7 +16,7 @@ INSERT INTO playlist_tracks (
     phantom_title, phantom_artist, phantom_album,
     phantom_duration_ms, phantom_genre, phantom_cover_art_path
 ) VALUES (?, ?, ?, ?, ?, ?, ?, ?, ?)
-RETURNING id, playlist_id, audio_file_id, position, phantom_title, phantom_artist, phantom_album, phantom_duration_ms, phantom_genre, phantom_cover_art_path
+RETURNING id, playlist_id, audio_file_id, position, phantom_title, phantom_artist, phantom_album, phantom_duration_ms, phantom_genre, phantom_cover_art_path, phantom_file_path
 `
 
 type AddPlaylistTrackParams struct {
@@ -55,6 +55,7 @@ func (q *Queries) AddPlaylistTrack(ctx context.Context, arg AddPlaylistTrackPara
 		&i.PhantomDurationMs,
 		&i.PhantomGenre,
 		&i.PhantomCoverArtPath,
+		&i.PhantomFilePath,
 	)
 	return i, err
 }