- CRITICAL: Change DNS zones endpoint from GET to POST to avoid
leaking API token in URL query parameters
- HIGH: Add sync.RWMutex to protect dnsProvider field in Server,
Deployer, and proxy Manager against concurrent read/write races
- HIGH: Capture old DNS provider reference synchronously before
launching background cleanup goroutine
- HIGH: Use getDNS()/getDNSProviderLocked() accessors instead of
direct field reads in all DNS operations
