feat: initial GitOps infrastructure

ArgoCD app definitions, Kustomize manifests for health-app,
cert-manager ClusterIssuer, and AppProject configuration.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

environments/health-app/overlays/production/kustomization.yaml

@@ -0,0 +1,18 @@
+apiVersion: kustomize.config.k8s.io/v1beta1
+kind: Kustomization
+
+resources:
+  - ../../base
+
+images:
+  - name: ghcr.io/infinicaretech/health-app
+    newTag: latest
+
+patches:
+  - target:
+      kind: Deployment
+      name: health-app
+    patch: |-
+      - op: replace
+        path: /spec/replicas
+        value: 2