Replace per-request GetByKey calls with a singleflight-backed
RuntimeSettings snapshot loaded via ListSystemConfigsByKeys.
Invalidate snapshot on admin cap_* writes and via Redis pub/sub.
Simplify VerifyMiddleware and update PERFORMANCE.md status.
- Extract isOriginAllowed helper to match Origin against server_address configurations
- Ensure arbitrary origins are not reflected and credentials are not allowed when server_address is unconfigured or mismatched
- Trim trailing slashes from allowed origins configuration for robust matching
- Add TestCORSMiddleware to cover all CORS matching and rejection scenarios