refactor: lazy load credentials for testing

tests/conftest.py

@@ -1,3 +1,13 @@
+import pytest
+
 from lrx_cli.config import enable_debug
 
 enable_debug()
+
+
+@pytest.fixture
+def no_credentials(monkeypatch):
+    """Clear all credential env vars so only anonymous fetchers are active."""
+    monkeypatch.delenv("SPOTIFY_SP_DC", raising=False)
+    monkeypatch.delenv("QQ_MUSIC_API_URL", raising=False)
+    monkeypatch.delenv("MUSIXMATCH_USERTOKEN", raising=False)