Add UI editing for local DNS zones

Local zones were only editable as mounted files, so operators could not manage DNS entries from the console. Add a Local zones editor backed by a shared Kubernetes ConfigMap, validate master files before saving, scope the pod service account to that ConfigMap, and reload changed zones on every replica while flushing stale cache entries.

deploy/k8s/10-deployment.yaml

@@ -27,6 +27,7 @@ spec:
       annotations:
         k8s-helper.io/git-url: "https://git.k6n.net/mats/fancy-dns"
         k8s-helper.io/git-ssh: "git@git.k6n.net:mats/fancy-dns.git"
+        dns.k6n.net/zones-api: "enabled"
         # A config change is a SIGHUP, not a restart: the server re-reads the
         # file and hot-swaps every component. This annotation is for
         # stakater/reloader-class controllers; without one, `kubectl rollout
@@ -152,15 +153,13 @@ spec:
         - name: config
           configMap:
             name: fancy-dns-config
-    # Local zones are ordinary master files; ship them in a ConfigMap or
-    # edit them in the mounted volume. There is no zone API — the admin API
-    # drives blocklists, the cache and the query log, not the zone files.
-        # the data volume. Optional because the glob in the config matches
-        # nothing cleanly.
+        # Local zones are ordinary master files. The API writes them to the
+        # shared ConfigMap, which projects one zone--<apex>.zone file per zone here.
+        # The GitOps manifest creates the ConfigMap empty; the UI owns its data.
         - name: zones
           configMap:
             name: fancy-dns-zones
-            optional: true
+            optional: false
         - name: tls
           secret:
             secretName: fancy-dns-tls