Add HTTPS configuration with cert-manager

- cert-manager namespace
- ClusterIssuer for Let's Encrypt (prod and staging)
- HTTPS Ingress for ArgoCD, Gitea, and test-app
- Automatic certificate management

Co-Authored-By: Claude Sonnet 4.5 <noreply@anthropic.com>

manifests/01-namespace.yaml

@@ -0,0 +1,4 @@
+apiVersion: v1
+kind: Namespace
+metadata:
+  name: cert-manager