Add Build Remote Agent phone pairing (gbr/1)

[LinespottingPrivate]

Add a pairing-device adapter so a phone running Build Remote Agent can spectate this desktop session.

Protocol stays gbr/1 (no fourth pair protocol). Pair with gbr-agent pair (browser QR and printed 8-char code) then gbr-agent run. Attach only:

• HTTP Bot API http://127.0.0.1:8788
• MCP stdio gbr-mcp

The phone is spectator + veto, not orchestrator. No mailbox keys in this PR.

Docs: https://grokbuildremote.com/
Agent (MIT): https://github.com/LinespottingOrg/GrokBuildRemote-Agents

Independent product by Linespotting AB. Not affiliated with xAI or SpaceX.

[CLAassistant]

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