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/base/httproute.yaml

@@ -0,0 +1,19 @@
+apiVersion: gateway.networking.k8s.io/v1
+kind: HTTPRoute
+metadata:
+  name: myapp-route
+  labels:
+    app: myapp
+    managed-by: argocd
+spec:
+  parentRefs:
+  - name: cluster-gateway
+    namespace: traefik-system
+  rules:
+  - matches:
+    - path:
+        type: PathPrefix
+        value: /
+    backendRefs:
+    - name: myapp
+      port: 80