docs(oauth): record live MCP canary

[halfaipg]

Summary

• replace the dark rollout snapshot with immutable production evidence
• record the authenticated, paid, load, SSE, and rollback canaries
• clarify that disabled OAuth keeps loopback introspection available only to return tokens inactive

Verification

• git diff --check
• OAuth service/route suite: 14 passed
• production release 4e744fee live and healthy