Feat: Add Kubernetes manifests for k3s production deployment

Adds complete k8s/ manifest tree: Namespace, VaultAuth + VaultStaticSecret
CRDs (VSO secret sync from Vault KV v2), API and UI Deployments and Services,
nginx Ingress with cert-manager TLS, MinIO StatefulSet with PVC and init Job,
and Alembic init container on the API Deployment for automatic schema
migrations. Includes .yamllint.yml config and validate-k8s Makefile target.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

k8s/api/service.yaml

@@ -0,0 +1,13 @@
+apiVersion: v1
+kind: Service
+metadata:
+  name: api
+  namespace: reactbin
+spec:
+  type: ClusterIP
+  selector:
+    app: api
+  ports:
+    - name: http
+      port: 8000
+      targetPort: 8000