infra(k8s): add dev overlay with resource limits and health checks

Implements Task 25: Kustomize Dev Overlay + Resource Limits + Health Checks

Files Created:
- infra/k8s/overlays/dev/kustomization.yaml - Dev overlay config
  - References base manifests
  - Namespace: workclub-dev
  - Replicas: 1 for all deployments
  - Image tags: dev for workclub-api and workclub-frontend
  - Environment label: development

- infra/k8s/overlays/dev/patches/backend-resources.yaml
  - Backend resources: cpu=50m-200m, memory=128Mi-256Mi
  - Strategic merge patch targeting workclub-api deployment

- infra/k8s/overlays/dev/patches/frontend-resources.yaml
  - Frontend resources: cpu=50m-200m, memory=128Mi-256Mi
  - Strategic merge patch targeting workclub-frontend deployment

- frontend/src/app/api/health/route.ts
  - Missing health endpoint (declared in base manifest but not implemented)
  - Simple Next.js route handler returning {status: 'ok'}

Resource Limits (Dev vs Base):
- Dev: 50m-200m CPU, 128Mi-256Mi memory (50% of base)
- Base: 100m-500m CPU, 256Mi-512Mi memory

Verification:
- kustomize build succeeds (exit 0)
- All deployments replicas=1
- Lower resource limits applied correctly
- Image tags set to dev
- Frontend /api/health route registered
- Evidence saved to .sisyphus/evidence/task-25-kustomize-dev.yaml (495 lines)

Note: commonLabels deprecated warning (non-blocking), consider using labels in future.

infra/k8s/overlays/dev/kustomization.yaml

@@ -0,0 +1,32 @@
+apiVersion: kustomize.config.k8s.io/v1beta1
+kind: Kustomization
+
+resources:
+  - ../../base
+
+namespace: workclub-dev
+
+commonLabels:
+  environment: development
+
+images:
+  - name: workclub-api
+    newTag: dev
+  - name: workclub-frontend
+    newTag: dev
+
+replicas:
+  - name: workclub-api
+    count: 1
+  - name: workclub-frontend
+    count: 1
+
+patches:
+  - path: patches/backend-resources.yaml
+    target:
+      kind: Deployment
+      name: workclub-api
+  - path: patches/frontend-resources.yaml
+    target:
+      kind: Deployment
+      name: workclub-frontend