docs: resource health-checks and rate-limit/quota recovery patterns

[mastermanas805]

Summary

• Documents GET /api/v1/resources and GET /api/v1/resources/:token endpoints with status semantics
• Adds connectivity verification examples (psql/redis-cli/mongosh ping patterns) for agent use
• Documents TTL awareness pattern — surfacing expires_at + claim URL to users
• Documents anonymous fingerprint dedup behavior (6th provision returns existing token, not 429)
• Documents 402 quota-exhaustion shape, 429 rate-limit retry field, and full error-code reference table

Test plan

• Verify llms.txt renders correctly at instanode.dev/llms.txt after merge + redeploy