Unofficial Apple Music MCP v0.2.1

Fixed

• The direct library add refused a rail it could see. config(action='status')
  reported catalog adds as ready while library(action='add') answered "this
  build ships no MusicKit helper" — both from the same process, seconds apart.
  Reported from the field against 0.2.0.

  _library_add was the one site converted in 0.2.0 that got the new message
  without the new routing: its error text pointed at config(action='signin')
  while its gate still asked only about developer tokens, so a MusicKit-only
  host was refused. It now checks both rails like the other sites, and its adds
  go through the rail-aware helpers instead of calling the token rail directly.

• The setup hint could deny a helper it could see. _musickit_setup_hint
  looked the authorization status up in a dict whose default was "this build
  ships no MusicKit helper" — and authorized was not a key, so an authorized
  helper produced the one message guaranteed to be wrong. "No helper" is now
  reachable only when there is genuinely no helper, and an unrecognised status
  names itself rather than being guessed at.

• Two silent false negatives in catalog search. _search_catalog_songs and
  _search_catalog_albums called get_headers() inside a bare except that
  returned [], which every caller reads as "not in the catalog". On a host
  with no developer token that turned "you have no token" into "that song does
  not exist", with no error surfaced. Both take the public rail first now, so
  library(action='add', track=…) and album=… work without a credential.