Reformat every module with autopep8 and hand-tune the remaining long
lines so that `flake8` passes with default settings (max line length
79). No behavior changes: long f-strings, messages, QSS/Textual CSS
rules and argument lists are only wrapped or split, an unused import
and an unused local are dropped, and dbus-next D-Bus signature
annotations carry targeted `# noqa` comments.
Register a session D-Bus MPRIS service (org.mpris.MediaPlayer2.mtsmusic)
in both the TUI and Qt apps, so the player shows up as a media source:
play/pause, next/previous, seek, metadata (title/artist/album/length/art)
and volume can be controlled from the GNOME media-controls extension,
playerctl and other MPRIS clients. Integration is optional and degrades
to a no-op without dbus-next or a session bus.
