chore(openapi): sync mutation rate-limit responses

[tiankaima]

Summary

• sync the OpenAPI contract from feat(api): add application mutation rate limits server#444
• regenerate the Go client with typed 429/503 mutation responses and Retry-After headers
• include the final 500-item subscription batch bounds

The matching server branch uses the same agent/issue-414-rate-limit-openapi name so the cross-repository drift check resolves the PR contract instead of server main.

Verification

• make generate
• make test
• git diff --check
• copied OpenAPI blob SHA: 168e728f8c5735eefae4d036a03b0df6433b5c0d

Tracks Life-USTC/server#414 and Life-USTC/server#444.