Add Flux CD GitOps sync for alaska/core stacks

Prepares clusters/production/ for `flux bootstrap git` - Kustomizations
for manifests/alaska and manifests/core, plus a Gitea push Receiver so
new commits reconcile immediately instead of waiting on the poll
interval. Webhook exposed on a dedicated host (flux-webhook.workolik.com)
to avoid the existing queue.workolik.com Gateway/Ingress overlap.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>

clusters/production/webhook-receiver.yaml

@@ -0,0 +1,17 @@
+# The referenced Secret (gitea-webhook-token) is created directly on the
+# cluster, not committed here - see the server-side command sequence.
+apiVersion: notification.toolkit.fluxcd.io/v1
+kind: Receiver
+metadata:
+  name: gitea-receiver
+  namespace: flux-system
+spec:
+  type: gitea
+  events:
+    - push
+  secretRef:
+    name: gitea-webhook-token
+  resources:
+    - apiVersion: source.toolkit.fluxcd.io/v1
+      kind: GitRepository
+      name: flux-system