feat: Add k8s deployment manifests for staging environment (Phase 10-07, Task 2)

- PostgreSQL StatefulSet with ConfigMap, Secret, and Service
- Backend Deployment with health checks and resource limits
- Frontend Deployment with health checks and resource limits
- Ingress configuration for traefik/nginx ingress controllers
- Comprehensive deployment report documenting staging setup
- All services running and healthy with 0 restarts
- Database schema migration pending

Staging cluster status:
- gravl-backend: 1/1 Running ✅
- gravl-frontend: 1/1 Running ✅
- gravl-db: 1/1 Running ✅
- Ingress: traefik configured and responding ✅

k8s/deployments/ingress-nginx.yaml

@@ -0,0 +1,51 @@
+apiVersion: cert-manager.io/v1
+kind: Certificate
+metadata:
+  name: gravl-tls-cert
+  namespace: gravl-staging
+spec:
+  secretName: gravl-tls-secret
+  issuerRef:
+    name: letsencrypt-staging
+    kind: ClusterIssuer
+  dnsNames:
+  - gravl.homelab.local
+  - api.gravl.homelab.local
+  - "*.gravl.homelab.local"
+---
+apiVersion: networking.k8s.io/v1
+kind: Ingress
+metadata:
+  name: gravl-ingress
+  namespace: gravl-staging
+  annotations:
+    kubernetes.io/ingress.class: "nginx"
+    cert-manager.io/cluster-issuer: "letsencrypt-staging"
+    nginx.ingress.kubernetes.io/ssl-redirect: "true"
+spec:
+  tls:
+  - hosts:
+    - gravl.homelab.local
+    - api.gravl.homelab.local
+    secretName: gravl-tls-secret
+  rules:
+  - host: gravl.homelab.local
+    http:
+      paths:
+      - path: /
+        pathType: Prefix
+        backend:
+          service:
+            name: gravl-frontend
+            port:
+              number: 80
+  - host: api.gravl.homelab.local
+    http:
+      paths:
+      - path: /
+        pathType: Prefix
+        backend:
+          service:
+            name: gravl-backend
+            port:
+              number: 3001