Add Kubernetes/K3s deployment manifests and documentation

- Complete k8s manifests with Kustomize support
- Production and staging overlays
- ConfigMap/Secret management
- Ingress with TLS (Traefik/NGINX)
- Persistent storage for SQLite
- Comprehensive k8s README with operations guide
- Updated main README with k8s deployment instructions
- Gitignore for k8s secrets

Usage:
  kubectl apply -k k8s/overlays/production

k8s/base/kustomization.yaml

@@ -0,0 +1,17 @@
+apiVersion: kustomize.config.k8s.io/v1beta1
+kind: Kustomization
+
+resources:
+  - deployment.yaml
+  - configmap.yaml
+  - ingress.yaml
+
+commonLabels:
+  app.kubernetes.io/name: dyn-ddns
+  app.kubernetes.io/part-of: dws-dns
+
+namespace: default
+
+images:
+  - name: git.dws.rip/DWS/dyn
+    newTag: latest