feat(dns): implement Cloudflare providerCloudflare dns provider

[marklao666888]

Summary

• replace the Cloudflare DNS stub with real Cloudflare API v4 calls
• implement zone listing, record listing, create/update upsert, delete, and round-robin A record syncing
• map Cloudflare records into the shared DnsRecord shape, including TTL and proxied state
• add tests for auth requirements, zone/record mapping, create/update, round-robin diffing, and API errors

Part of #6.

Testing

• Not run locally: this environment only has node.exe; npm, pnpm, corepack, and tsc are not installed.