fix(audio): remove vocal bleed with instrumental-only mix

tests/test_main_cli.py

@@ -2,6 +2,8 @@
 
 from __future__ import annotations
 
+from src.audio_separation import DEFAULT_MIX_MODE
+
 from main import _build_translation_config, build_parser
 
 
@@ -59,3 +61,11 @@ def test_translation_config_uses_env_defaults(monkeypatch):
     assert config.base_url == "http://env-host:1234/v1"
     assert config.model == "env-model"
     assert config.api_key == "env-key"
+
+
+def test_parser_defaults_to_instrumental_only_mix_mode():
+    parser = build_parser()
+
+    args = parser.parse_args(["https://youtube.com/watch?v=demo"])
+
+    assert args.mix_mode == DEFAULT_MIX_MODE