chore(deploy): promote production to 1.8.1

[rdimitrov]

Summary

Promote the production registry image from 1.8.0 to 1.8.1.

This release includes #1509, which adds a short ingress cache and a scoped rate-limit increase for the exact public registry-list endpoints.

Staging verification

• release tag points to f52dc8525a441a3abf5fedc9912152d95af5aab1, the commit deployed to staging
• staging deployment and CI workflows completed successfully
• both registry replicas became ready with zero restarts
• rendered NGINX configuration kept the root route at 180 RPM with buffering off
• exact /v0/servers and /v0.1/servers routes rendered at 600 RPM with buffering on
• live cache probe returned MISS, then HIT
• health and unrelated routes remained uncached
• no application 5xx, serious NGINX errors, or application error logs were observed after rollout

Release artifact

• release workflow completed successfully
• ghcr.io/modelcontextprotocol/registry:1.8.1 is available for linux/amd64 and linux/arm64

Deployment and rollback

Merging this PR triggers the production Pulumi deployment automatically. Monitor registry pod readiness, NGINX reloads, cache behavior, origin request volume, 429/499/5xx responses, and publish requests exceeding 10 seconds.

Rollback by restoring mcp-registry:imageTag to 1.8.0.