feat: restructure GitOps for multi-environment deployment

- Add apps/myapp/base with deployment, service, httproute
- Add apps/myapp/overlays/staging (1 replica, 128Mi/256Mi, staging hostname)
- Add apps/myapp/overlays/production (2 replicas, 256Mi/512Mi, prod hostname)
- Remove old apps/sample-webapp structure

Structure follows folder-per-environment pattern with Kustomize overlays.

apps/myapp/overlays/production/deployment-patch.yaml

@@ -0,0 +1,17 @@
+apiVersion: apps/v1
+kind: Deployment
+metadata:
+  name: myapp
+spec:
+  replicas: 2
+  template:
+    spec:
+      containers:
+      - name: myapp
+        resources:
+          requests:
+            memory: "256Mi"
+            cpu: "200m"
+          limits:
+            memory: "512Mi"
+            cpu: "500m"