Add Build Remote Agent phone pairing (gbr/1)

[LinespottingPrivate]

Pair a phone with Build Remote Agent

Adds a how-to so a phone running Build Remote Agent can spectate OpenCortexIDE/cortexide through free MIT gbr-agent.

• Protocol gbr/1 (agent v0.6.0+)
• Attach only Bot API http://127.0.0.1:8788 after gbr-agent run, or MCP stdio gbr-mcp
• Phone is spectator + veto, not orchestrator
• No mailbox keys in this PR

Install

curl -fsSL https://grokbuildremote.com/install.sh | bash
gbr-agent version   # v0.6.0+
gbr-agent pair && gbr-agent run
curl -sS http://127.0.0.1:8788/health

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