refactor(server): register loaded module in sys.modules, add __all__

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

tests/test_mf_loader.py

@@ -1,3 +1,6 @@
+"""Tests for the server.mf loader."""
+
+
 def test_mf_reexports_musicfetch_symbols():
     from server import mf
     assert hasattr(mf, "Hit")
@@ -6,6 +9,7 @@ def test_mf_reexports_musicfetch_symbols():
     assert callable(mf.act_youtube)
     assert callable(mf.act_lidarr_album)
     assert callable(mf.act_lidarr_artist)
+    assert isinstance(mf.QUALITY_CHOICES, list)
 
 
 def test_mf_hit_constructs():