Polish AgentRouter Pully integration

[fschrhunt]

Summary

• support multiple private GitHub Apps from one AgentRouter runtime
• expose an authenticated Pully open-PR feed backed by installed GitHub App repositories
• ping Pully's local event endpoint when GitHub webhooks arrive
• route the third lane as Huma/OpenClaw instead of local
• add a main-backed LaunchAgent installer for AgentRouter

Verification

• pnpm verify

Notes

• This does not merge anything. After Fischer merges, run AgentRouter from /Volumes/Thorium/Projects/AgentRouter/main and install the LaunchAgent from main.