fix: add transcription model fallback chain

tests/test_openrouter_client.py

@@ -5,7 +5,7 @@ from pathlib import Path
 
 sys.path.insert(0, os.path.dirname(os.path.dirname(__file__)))
 
-from openrouter_client import _audio_format, _build_transcription_payload
+from openrouter_client import TRANSCRIPTION_MODELS, _audio_format, _build_transcription_payload
 
 
 def test_audio_format_defaults_to_wav_when_missing_suffix(tmp_path: Path):
@@ -18,9 +18,8 @@ def test_build_transcription_payload_uses_base64_json_shape(tmp_path: Path):
     path = tmp_path / "meeting.wav"
     path.write_bytes(b"RIFFdemo")
 
-    payload = _build_transcription_payload(str(path))
+    payload = _build_transcription_payload(str(path), TRANSCRIPTION_MODELS[0])
 
-    assert payload["model"] == "openai/whisper-large-v3"
-    assert payload["language"] == "en"
+    assert payload["model"] == "openai/gpt-4o-mini-transcribe"
     assert payload["input_audio"]["format"] == "wav"
     assert payload["input_audio"]["data"] == base64.b64encode(b"RIFFdemo").decode("ascii")