Add P3 live camera streaming

[shaunbarrow]

Summary

• add hardware-verified P3 live camera transport over the WS-V2 media_stream channel
• map Home Assistant's P3 overview / closeup cameras to xTool Studio's far / upside live names
• bridge Annex-B H.264 through a localhost-only TCP source into Home Assistant's native Stream integration
• retain the existing snapshot-polled MJPEG fallback for models whose live transport has not been verified
• document the observed protocol and update the camera capability table

This follows the still-image repair documented in #10. It does not change job control or laser operation.

Root cause

The integration only exposed snapshot polling. Its protocol notes also assumed the media_stream channel required WebRTC signaling. Current xTool Studio code and live P3 traffic show a simpler direct path: Studio opens a same-session media_stream WebSocket, starts /v1/platform/camera/live, and receives protocol-34 frames containing a one-byte stream id followed by Annex-B H.264.

Safety and scope

• Live support is explicitly allowlisted for P3 only.
• The decoder source listens on 127.0.0.1 with an ephemeral port; it is not exposed to the LAN.
• Start/stop requests are paired in try/finally cleanup.
• Existing still images and fallback behavior remain unchanged for other models.

Validation

• git diff --check
• Python 3.12 compileall over custom_components/xtool
• JSON parse validation for manifest.json
• live P3 hardware probe: start and stop returned success; protocol-34 H.264 decoded as High profile, 1280x720, approximately 10 delivered packets/frames per second
• captured Annex-B stream decoded to a valid first frame with ffmpeg

HACS and hassfest validation will run in this repository's GitHub Actions workflow.