feat(M003/S01): play history tracking — schema, migration, recording hook

Migration 10:
- play_history table (audio_file_id FK, played_at DATETIME, CASCADE delete)
- play_count + last_played columns on audio_files (denormalized)
- Recreated track_metadata VIEW with play_count and last_played columns

Play recording:
- queue.recordPlay() inserts play_history row + updates denormalized columns
- Called from OnPlaybackFinished after queue advance completes
- Mutex released before DB write to avoid MaxOpenConns(1) deadlock
- Natural finish only — skip/stop does not count

Tests:
- TestMigration10PlayHistory: schema, columns, VIEW, round-trip verification
- All 49 smart playlist + 15 service + existing DB tests still pass

backend/database/database.go

@@ -341,6 +341,14 @@ func runMigrations(
 		}
 	}
 
+	if version < 10 {
+		if err := migration10PlayHistory(
+			ctx, db, logger,
+		); err != nil {
+			return err
+		}
+	}
+
 	return nil
 }
 
@@ -1211,6 +1219,139 @@ func migration9SmartPlaylists(
 	return nil
 }
 
+// migration10PlayHistory adds play history tracking:
+// - play_history table for timestamped play log
+// - play_count and last_played columns on audio_files
+// - Recreates track_metadata VIEW to expose the new columns
+func migration10PlayHistory(
+	ctx context.Context,
+	db *sql.DB,
+	logger *slog.Logger,
+) error {
+	logger.Info(
+		"applying migration 10: play history tracking",
+	)
+
+	// 1. Create play_history table.
+	if _, err := db.ExecContext(ctx, `
+		CREATE TABLE IF NOT EXISTS play_history (
+			id INTEGER PRIMARY KEY,
+			audio_file_id INTEGER NOT NULL,
+			played_at DATETIME NOT NULL DEFAULT (datetime('now')),
+			FOREIGN KEY(audio_file_id) REFERENCES audio_files(id) ON DELETE CASCADE
+		)`,
+	); err != nil {
+		return fmt.Errorf(
+			"migration 10: could not create play_history table: %w",
+			err,
+		)
+	}
+
+	if _, err := db.ExecContext(ctx, `
+		CREATE INDEX IF NOT EXISTS idx_play_history_audio_file_id
+		ON play_history(audio_file_id)`,
+	); err != nil {
+		return fmt.Errorf(
+			"migration 10: could not create play_history index: %w",
+			err,
+		)
+	}
+
+	// 2. Add play_count and last_played columns to audio_files.
+	if _, err := db.ExecContext(ctx,
+		`ALTER TABLE audio_files
+		 ADD COLUMN play_count INTEGER NOT NULL DEFAULT 0`,
+	); err != nil {
+		if !isDuplicateColumnErr(err) {
+			return fmt.Errorf(
+				"migration 10: could not add play_count column: %w",
+				err,
+			)
+		}
+	}
+
+	if _, err := db.ExecContext(ctx,
+		`ALTER TABLE audio_files
+		 ADD COLUMN last_played DATETIME`,
+	); err != nil {
+		if !isDuplicateColumnErr(err) {
+			return fmt.Errorf(
+				"migration 10: could not add last_played column: %w",
+				err,
+			)
+		}
+	}
+
+	// 3. Recreate track_metadata VIEW to include play_count and last_played.
+	if _, err := db.ExecContext(
+		ctx, "DROP VIEW IF EXISTS track_metadata",
+	); err != nil {
+		return fmt.Errorf(
+			"migration 10: could not drop track_metadata VIEW: %w",
+			err,
+		)
+	}
+
+	if _, err := db.ExecContext(ctx, `
+		CREATE VIEW IF NOT EXISTS track_metadata AS
+		SELECT
+			af.id,
+			af.file_path,
+			af.length_milliseconds,
+			COALESCE(r.name, '') AS title,
+			COALESCE(ac.text, '') AS artist_name,
+			r.track_number,
+			r.disc_number,
+			COALESCE(rg.name, '') AS album,
+			CAST(COALESCE(
+				(SELECT GROUP_CONCAT(g.name, '||')
+				 FROM recording_genres rg_sub
+				 JOIN genres g ON rg_sub.genre_id = g.id
+				 WHERE rg_sub.recording_id = r.id),
+				''
+			) AS TEXT) AS genre,
+			COALESCE(r.year, 0) AS year,
+			COALESCE(r.composer, '') AS composer,
+			COALESCE(ft.extension, '') AS file_type,
+			af.sample_rate,
+			af.bit_depth,
+			af.channels,
+			af.bitrate,
+			af.file_size,
+			af.library_id,
+			af.play_count,
+			af.last_played
+		FROM audio_files af
+		LEFT JOIN recordings r ON af.recording_id = r.id
+		LEFT JOIN artist_credit ac ON r.artist_credit_id = ac.id
+		LEFT JOIN (
+			SELECT recording_id,
+				MIN(release_group_id) AS release_group_id
+			FROM release_group_recordings
+			GROUP BY recording_id
+		) rgr ON r.id = rgr.recording_id
+		LEFT JOIN release_groups rg ON rgr.release_group_id = rg.id
+		LEFT JOIN file_types ft ON af.file_type_id = ft.id`,
+	); err != nil {
+		return fmt.Errorf(
+			"migration 10: could not create track_metadata VIEW: %w",
+			err,
+		)
+	}
+
+	if _, err := db.ExecContext(
+		ctx, "PRAGMA user_version = 10",
+	); err != nil {
+		return fmt.Errorf(
+			"could not set user_version to 10: %w", err,
+		)
+	}
+
+	logger.Info("migration 10 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 {