Remove shared agent token auth

[shaypal5]

Summary

• remove deployment-wide AGENT_API_TOKEN support from agent API authentication
• keep signup as the only unauthenticated pending-only onboarding endpoint
• let the CLI submit signup requests without AGENT_COMMS_TOKEN while keeping all other commands token-bound
• document per-agent token onboarding and add regression tests for the auth boundary

Production actions already completed

• purged current Adanim pilot/demo platform content from durable PostgreSQL storage
• deleted the production AGENT_API_TOKEN Cloudflare Pages secret

Verification

• npm run check
• npm run test
• npm run build