feat: Add camera livestream and voice call support

Adds a standalone camera module for streaming video/audio from Roborock
vacuums with cameras. This addresses part of #738.

Features:
- Live video streaming (HD/SD quality)
- Bidirectional voice calls (speak to and hear from robot)
- Snapshot capture
- Video recording
- Audio sending for intercom functionality

The implementation uses:
- MQTT for WebRTC signaling (via existing protocol encoders)
- aiortc for WebRTC peer connection
- paho-mqtt for MQTT connection (standalone, not using aiomqtt)

This is provided as a standalone module that could be integrated more
tightly with the library's session management in future work.

See docs/CAMERA_PROTOCOL.md for full protocol documentation.

New dependencies (optional):
- aiortc: WebRTC implementation
- paho-mqtt: MQTT client
- pyaudio: Voice call audio (optional)
- opencv-python: Video display (optional)

Author: clawd139

docs/CAMERA_PROTOCOL.md

@@ -0,0 +1,179 @@
+# Roborock Camera Protocol Documentation
+
+This document describes the protocol for streaming video/audio from Roborock vacuum cameras.
+
+## Overview
+
+The camera uses **MQTT for signaling** and **WebRTC for media transport**:
+
+```
+┌─────────────┐     MQTT      ┌──────────────┐
+│   Client    │◄────────────►│  Roborock    │
+│  (Python)   │   Signaling   │   Cloud      │
+└─────────────┘               └──────────────┘
+       │                             │
+       │         WebRTC              │
+       └─────────────────────────────┘
+              Video + Audio
+```
+
+## Connection Flow
+
+1. Connect to MQTT broker (`mqtt-{region}.roborock.com:8883`)
+2. Authenticate with password hash
+3. Start camera preview
+4. Get TURN server credentials from Roborock cloud
+5. Exchange SDP/ICE candidates via MQTT
+6. Establish WebRTC peer connection
+7. Receive video/audio tracks
+
+## MQTT Topics
+
+```
+Publish:  rr/m/i/{rriot_u}/{client_id}/{duid}
+Subscribe: rr/m/o/{rriot_u}/{client_id}/{duid}
+```
+
+Where:
+- `rriot_u`: User identifier from Roborock account
+- `client_id`: MD5-derived client identifier
+- `duid`: Device unique identifier
+
+## MQTT Credentials
+
+```python
+mqtt_username = md5(f"{rriot_u}:{rriot_k}")[2:10]
+mqtt_password = md5(f"{rriot_s}:{rriot_k}")[16:]
+```
+
+## Commands
+
+All commands are sent via protocol 101 in the `dps.101` field. Responses come in `dps.102`.
+
+### Camera Control
+
+| Command | Params | Response | Notes |
+|---------|--------|----------|-------|
+| `check_homesec_password` | `{password: md5_hash}` | `['ok']` | Authenticate with pattern password |
+| `start_camera_preview` | `{client_id, quality, password}` | `['ok']` | Begin video session |
+| `stop_camera_preview` | `[]` | `['ok']` | End video session |
+| `switch_video_quality` | `{quality: "HD"/"SD"}` | `['ok']` | Change resolution |
+
+### WebRTC Signaling
+
+| Command | Params | Response | Notes |
+|---------|--------|----------|-------|
+| `get_turn_server` | `[]` | `{url, user, pwd}` | TURN credentials |
+| `send_sdp_to_robot` | `{app_sdp: base64}` | `['ok']` | Send our SDP offer |
+| `get_device_sdp` | `[]` | `{dev_sdp: base64}` or `"retry"` | Robot's SDP answer |
+| `send_ice_to_robot` | `{app_ice: base64}` | `['ok']` | Send ICE candidates |
+| `get_device_ice` | `[]` | `{dev_ice: [base64...]}` | Robot's ICE candidates |
+
+### Voice Chat
+
+| Command | Params | Response | Notes |
+|---------|--------|----------|-------|
+| `start_voice_chat` | `[]` | `['ok']` | Enable bidirectional audio |
+| `stop_voice_chat` | `[]` | `['ok']` | Disable audio |
+
+**Important:** Without calling `start_voice_chat`, the audio track exists but sends no frames!
+
+### Remote Control
+
+| Command | Params | Response | Notes |
+|---------|--------|----------|-------|
+| `app_rc_start` | `[]` | `['ok']` | Begin RC session |
+| `app_rc_move` | `{omega, velocity, seqnum, duration}` | `['ok']` | Movement command |
+| `app_rc_end` | `[]` | `['ok']` | End RC session |
+
+RC Parameters:
+- `velocity`: Forward/backward speed (±0.2 typical range)
+- `omega`: Rotation speed in rad/s (±0.53 typical range)
+- `seqnum`: Incrementing sequence number
+- `duration`: Command duration in ms (500 typical)
+
+## Audio Format
+
+### Robot → Client
+- **Format:** Stereo interleaved, 48kHz, 16-bit signed PCM
+- **Frame size:** 960 samples per channel (20ms)
+- **Raw frame:** 1920 int16 values in LRLRLR... pattern
+- **To extract mono:** `audio[::2]` (take left channel)
+
+### Client → Robot
+- **Format:** Mono, 48kHz, 16-bit signed PCM
+- **Frame size:** 960 samples (20ms)
+- **Timing:** Send frames spaced ~18-20ms apart
+
+## Message Format
+
+### Request (dps.101)
+```json
+{
+  "id": 100001,
+  "method": "command_name",
+  "params": {}
+}
+```
+
+### Response (dps.102)
+```json
+{
+  "id": 100001,
+  "result": ["ok"]
+}
+```
+
+Or on error:
+```json
+{
+  "id": 100001,
+  "error": {"code": -1, "message": "error description"}
+}
+```
+
+## SDP/ICE Format
+
+SDP and ICE candidates are base64-encoded JSON:
+
+```python
+# SDP
+sdp_json = json.dumps({"sdp": sdp_string, "type": "offer"})
+sdp_b64 = base64.b64encode(sdp_json.encode()).decode()
+
+# ICE
+ice_json = json.dumps({
+    "candidate": "candidate:...",
+    "sdpMid": "0",
+    "sdpMLineIndex": 0
+})
+ice_b64 = base64.b64encode(ice_json.encode()).decode()
+```
+
+## Important Notes
+
+1. **One session at a time** - Only one client can preview the camera. Close the phone app first.
+
+2. **Password rate limiting** - Too many incorrect password attempts may disable remote viewing temporarily.
+
+3. **TURN server required** - NAT traversal typically requires the TURN server; direct P2P connections are rare.
+
+4. **Pattern password** - The password is your numeric pattern (e.g., "9876"), not your Roborock account password.
+
+## Tested Devices
+
+- Roborock Qrevo Curv (model a135)
+
+Other camera-equipped Roborock models likely use the same protocol but are untested.
+
+## Getting Credentials
+
+The required credentials (`duid`, `local_key`, `rriot_u/k/s`) can be obtained from:
+- Home Assistant's Roborock integration storage
+- The python-roborock library's login flow
+- Roborock app traffic analysis
+
+## References
+
+- [python-roborock](https://github.com/Python-roborock/python-roborock) - Protocol encoding/decoding
+- [aiortc](https://github.com/aiortc/aiortc) - Python WebRTC implementation