- Add overlay modal for browsing sibling video files and live mpv queue
- Add IPC commands for playlist operations (add, remove, move, play)
- Add playlist-browser-runtime and playlist-browser-sort modules
- Add keyboard handler and preload bindings for playlist browser
- Add default Ctrl+Alt+P keybinding to open the modal
- Add HTML structure, renderer wiring, and state for the modal
- Add changelog fragment and docs updates
