feat(cli): completions, library/audio commands, server switcher

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.

src-tauri/Cargo.lock

@@ -3615,6 +3615,7 @@ dependencies = [
  "tokio",
  "url",
  "windows 0.58.0",
+ "zbus 5.14.0",
 ]
 
 [[package]]