feat: SaluteSpeech STT for the pilot + no foreign STT outside the demo (ADR-016)

Refs #121

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

app/api/patient_web.py

@@ -265,6 +265,8 @@ async def transcribe_voice(token: str, request: Request) -> SttOut:
     started = monotonic_time.monotonic()  # latency only, not domain time (that is app.core.clock)
     try:
         text = await stt.transcribe(audio, "wav")
+    except InvalidAudio as exc:
+        raise HTTPException(415, "expected 16-bit mono PCM WAV") from exc
     except SttNoSpeech as exc:
         raise HTTPException(422, "no speech recognised") from exc
     except SttError as exc: