Embed bash and zsh completion scripts and add a `completions` subcommand.
Extend the player CLI (library, audio device, instant mix) and surface
`music_library` in snapshots. Add a shared active-server switcher in the
header and locales; instant mix can reseed the queue from CLI and UI.
- CI: add squashfs-tools dep, APPIMAGE_EXTRACT_AND_RUN=1, appimage to
--bundles, and *.AppImage to upload glob
- main.rs: set GDK_BACKEND=x11 and WEBKIT_DISABLE_COMPOSITING_MODE=1
on Linux before Tauri init — WebKitGTK on Wayland is unstable;
both vars are overridable by setting them before launch
Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>