Initial commit: audio-chat with fixes

- Created AGENTS.md with architecture documentation
- Fixed race conditions and async patterns
- Added conversation history to LLM prompts
- Fixed TTS audio shape handling
- Added buffer limits and graceful shutdown
- Fixed client.py with file sending support
- Removed duplicate requirements
- Added .gitignore

AGENTS.md

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+# Audio Chat
+
+## Running
+
+```bash
+uvicorn main:app --host 0.0.0.0 --port 8000
+```
+
+Client (for testing):
+```bash
+python client.py
+```
+
+## Architecture
+
+Single-process FastAPI server. On each WebSocket connection a new `AudioSession` is created with three engines:
+
+| Module | Purpose | Model (default) |
+|--------|---------|-----------------|
+| `engine/stt.py` | Speech-to-text | Systran/faster-whisper-large-v3 |
+| `engine/llm.py` | LLM response generation | Qwen/Qwen2.5-7B-Instruct |
+| `engine/tts.py` | Text-to-speech | facebook/mms-tts-rus |
+
+Models are loaded lazily on first use if `initialize()` was not called. STT always runs in Russian (`language="ru"` with VAD).
+
+## WebSocket Protocol
+
+| Direction | Format | Meaning |
+|-----------|--------|---------|
+| Client → Server | `b"A" + PCM data` | Send audio chunk |
+| Client → Server | `b"R"` | Reset conversation |
+| Server → Client | `b"O" + WAV bytes` | LLM response as audio |
+| Server → Client | `"TEXT:<transcription>"` | Recognized speech |
+
+Audio format: 16-bit PCM mono, 16 kHz input / 24 kHz output.
+
+## Configuration
+
+All settings via `.env` (loaded by `config.py`). Key vars:
+
+- `DEVICE` — `"cuda"` or `"cpu"` (default `"auto"`)
+- `AUDIO_BUFFER_SECONDS` / `CHUNK_SIZE` — silence detection thresholds
+- `LLM_MAX_TOKENS` / `LLM_TEMPERATURE` — generation parameters
+
+## Gotchas
+
+- No test suite or linting configured.
+- Models download on first use; ensure network access to HuggingFace.
+- `AudioSession` holds conversation history (last 6 turns) in memory — each WebSocket reconnect resets it.
+- Thread pool executor is fixed at 2 workers; concurrent heavy requests will queue.
+- TTS pipeline falls back to CPU (`device=-1`) if GPU initialization fails silently.