Expose telemetry APIs and enforce API key rate limits

[Makisuo]

Summary

• Expose v2 traces, logs, metrics, services, service map, and query endpoints
• Add stage-partitioned Cloudflare rate limiting for API-key-authenticated requests
• Document telemetry scopes, query behavior, rate-limit responses, and log identities
• Extend API key UI and test harnesses for telemetry scopes and rate-limit scenarios
• Improve CORS handling and accessibility labels

Testing

• Added HTTP coverage for rate-limit responses, fail-open behavior, session-token bypasses, and scope enforcement
• Existing v2 test harnesses updated with telemetry and limiter layers
• Not run (not requested)

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