Remove all user-facing references to the internal `legacyDNSMode` variable
name. Error messages now reuse the deprecated.Note.MessageWithLink() method
to provide consistent deprecation text with migration URLs. Other internal
jargon ("consume response state", "response_*") is replaced with
user-friendly descriptions.
Add two migration guide entries under 1.14.0: one for strategy → rule items,
one for address filter fields → evaluate with match_response.
- Add EnvName to four new deprecation constants so users can suppress
warnings via ENABLE_DEPRECATED_* environment variables
- Add comment explaining why applyDNSRouteOptions skips Strategy
- Use dns.RcodeToString in DNSResponseRCodeItem.String() for readability
- Remove redundant Fqdn(FqdnToDomain(domain)) round-trip