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/deployment.yaml

@@ -0,0 +1,86 @@
+apiVersion: apps/v1
+kind: Deployment
+metadata:
+  name: dyn-ddns
+  labels:
+    app: dyn-ddns
+spec:
+  replicas: 1
+  selector:
+    matchLabels:
+      app: dyn-ddns
+  template:
+    metadata:
+      labels:
+        app: dyn-ddns
+    spec:
+      containers:
+      - name: dyn-ddns
+        image: git.dws.rip/DWS/dyn:latest
+        imagePullPolicy: Always
+        ports:
+        - containerPort: 8080
+          name: http
+        envFrom:
+        - configMapRef:
+            name: dyn-ddns-config
+        - secretRef:
+            name: dyn-ddns-secrets
+        volumeMounts:
+        - name: data
+          mountPath: /data
+        resources:
+          requests:
+            memory: "64Mi"
+            cpu: "100m"
+          limits:
+            memory: "256Mi"
+            cpu: "500m"
+        livenessProbe:
+          httpGet:
+            path: /
+            port: 8080
+          initialDelaySeconds: 10
+          periodSeconds: 30
+          timeoutSeconds: 5
+          failureThreshold: 3
+        readinessProbe:
+          httpGet:
+            path: /
+            port: 8080
+          initialDelaySeconds: 5
+          periodSeconds: 10
+          timeoutSeconds: 3
+          failureThreshold: 3
+      volumes:
+      - name: data
+        persistentVolumeClaim:
+          claimName: dyn-ddns-data
+---
+apiVersion: v1
+kind: Service
+metadata:
+  name: dyn-ddns
+  labels:
+    app: dyn-ddns
+spec:
+  selector:
+    app: dyn-ddns
+  ports:
+  - port: 80
+    targetPort: 8080
+    name: http
+  type: ClusterIP
+---
+apiVersion: v1
+kind: PersistentVolumeClaim
+metadata:
+  name: dyn-ddns-data
+  labels:
+    app: dyn-ddns
+spec:
+  accessModes:
+    - ReadWriteOnce
+  resources:
+    requests:
+      storage: 1Gi