Add subtitles, playlist booklets, and safer production installs

[RetricSu]

Summary

• add timed subtitle parsing, MP3 embedding, playback display, and authorized YouTube subtitle download support
• add playlist booklets plus versioned playlist archive import/export for booklet, cover, and track metadata
• isolate development data from production data, migrate and back up SQLite safely, and add a guarded macOS installer
• ensure packaged release builds opt into the production data profile

Why

Bird Player is being used as a daily player, so subtitles and playlist context need to travel with the media while development and upgrades must not risk the production library database.

User impact

Users can download and view timed subtitles, maintain portable playlist booklets, and upgrade the installed application with database backup and rollback protection. Existing databases are migrated rather than rebuilt, and unknown/newer schemas are refused safely.

Validation

• cargo fmt --all -- --check
• cargo test --all-targets — 42 passed
• cargo bundle --release --features production-data
• git diff --check
• compared the installed macOS app with a fresh production build; executable differences are limited to toolchain path labels, Mach-O UUID, and signing metadata