feat: scaffold stentor-gateway with FastAPI voice pipeline

Initialize the stentor-gateway project with WebSocket-based voice
pipeline orchestrating STT → Agent → TTS via OpenAI-compatible APIs.

- Add FastAPI app with WebSocket endpoint for audio streaming
- Add pipeline orchestration (stt_client, tts_client, agent_client)
- Add Pydantic Settings configuration and message models
- Add audio utilities for PCM/WAV conversion and resampling
- Add health check endpoints
- Add Dockerfile and pyproject.toml with dependencies
- Add initial test suite (pipeline, STT, TTS, WebSocket)
- Add comprehensive README covering gateway and ESP32 ear design
- Clean up .gitignore for Python/uv project

stentor-gateway/tests/conftest.py

@@ -0,0 +1,34 @@
+"""Shared test fixtures for Stentor Gateway tests."""
+
+import pytest
+
+from stentor.config import Settings
+
+
+@pytest.fixture
+def settings() -> Settings:
+    """Test settings with localhost endpoints."""
+    return Settings(
+        stt_url="http://localhost:9001",
+        tts_url="http://localhost:9002",
+        agent_url="http://localhost:9003",
+        log_level="DEBUG",
+    )
+
+
+@pytest.fixture
+def sample_pcm() -> bytes:
+    """Generate 1 second of silent PCM audio (16kHz, mono, 16-bit)."""
+    import struct
+
+    num_samples = 16000  # 1 second at 16kHz
+    return struct.pack(f"<{num_samples}h", *([0] * num_samples))
+
+
+@pytest.fixture
+def sample_pcm_short() -> bytes:
+    """Generate 100ms of silent PCM audio."""
+    import struct
+
+    num_samples = 1600  # 100ms at 16kHz
+    return struct.pack(f"<{num_samples}h", *([0] * num_samples))