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/apps-core.yaml

@@ -0,0 +1,14 @@
+apiVersion: kustomize.toolkit.fluxcd.io/v1
+kind: Kustomization
+metadata:
+  name: core
+  namespace: flux-system
+spec:
+  interval: 10m
+  sourceRef:
+    kind: GitRepository
+    name: flux-system
+  path: ./manifests/core
+  prune: true
+  wait: true
+  timeout: 3m