docs: Document camera live view WebRTC signaling protocol for V1 vacuums

[Lash-L]

Summary

Adds comprehensive internal documentation for the reverse-engineered Roborock camera live streaming protocol in docs/CAMERA_PROTOCOL.md and links it from docs/README.md.

This is PR 1 of a multi-part series breaking down vacuum camera support into small, reviewable increments following discussion in #764 and #738.

Scope & Evidence

• Protocol family: Roborock V1 (pv=1.0).
• Feature flag: is_video_monitor_supported (bit mask 8, bit 3 of robotNewFeatures).
• Tested hardware: Roborock Qrevo Curv (model a135).
• Source: Reverse-engineered from mobile app live view captures and verified against a standalone test client.
• Changes: Documentation only; no library or runtime code changes and no new dependencies.

What is Documented

• Session flow: Complete authentication and WebRTC negotiation sequence (PIN MD5 validation -> TURN credentials -> SDP offer/answer -> ICE candidate exchange -> stream lifecycle -> teardown).
• Framing & transport: V1 JSON-RPC carried in dps["101"] / dps["102"], outer protocol headers (101 over MQTT, 4 over local TCP), and MQTT topic structures.
• Serialization: Base64-encoded UTF-8 JSON encapsulation for SDP offers/answers and ICE candidate structures.
• Commands: Parameter schemas and response structures for camera preview, video quality switching, TURN credential acquisition, two-way intercom, and remote driving.
• Media specifications: H.264 video codec and Opus audio wire transport (distinguished from decoded application PCM buffers).
• Operational considerations: Single-client session concurrency, PIN rate-limiting, and residential NAT traversal.

Review Notes

• Cross-references existing V1 documentation in docs/DEVICES.md, docs/V1_DEVICE_FEATURES.md, and docs/V1_API_COMMANDS.md.
• Reviewed and iterated with automated analysis to ensure protocol framing, topic segments, and command schemas match the library's existing transport abstractions.