fix(external-dns): exclude internal records from Cloudflare, add opt-in filter, set targets

- external-dns-cloudflare: add excludeDomains: [local.mk-labs.cloud] to stop
  internal subdomain records from leaking to Cloudflare
- external-dns-cloudflare: replace hostname annotationFilter with opt-in model
  (external-dns.alpha.kubernetes.io/public=true) so only explicitly tagged
  services get public Cloudflare records
- external-dns-cloudflare: add extraArgs --target=lb.mk-labs.cloud
- external-dns (Technitium/rfc2136): add extraArgs
  --target=lightning-lane.local.mk-labs.cloud for internal records
- couchdb: add external-dns.alpha.kubernetes.io/public: 'true' annotation —
  first service to opt in to public DNS; will create communicore.mk-labs.cloud
  pointing to lb.mk-labs.cloud via Cloudflare ExternalDNS

URGENT: Cloudflare was creating records for local.mk-labs.cloud hosts.
Ryan: manually delete any *.local.mk-labs.cloud records currently in Cloudflare
(look for communicore.local.mk-labs.cloud and any other local.* entries).

cluster/platform/external-dns/values.yaml

@@ -45,6 +45,10 @@ sources:
 # external-dns.alpha.kubernetes.io/hostname: myservice.local.mk-labs.cloud
 annotationFilter: "external-dns.alpha.kubernetes.io/hostname"
 
+# Override the target for all Technitium-managed records to the internal LB hostname.
+extraArgs:
+  - --target=lightning-lane.local.mk-labs.cloud
+
 # Log level — info in normal ops, debug when troubleshooting
 logLevel: info