feat: SOPS + age encrypted secrets structure

- .sops.yaml with 3 age keys (admin, dev, prod)
- infra/gitea/values/*.enc.yaml — per-env encrypted Helm values
- infra/kargo/values/*.enc.yaml — per-env encrypted Kargo admin secrets
- kargo/credentials/*.enc.yaml — per-env encrypted git credentials (ksops)
- infra/kargo-credentials/ — ArgoCD app for deploying Kargo creds via ksops
- All repoURLs point to deploy-app-kargo-private

Structure from deploy-app-kargo (reference), adapted for SOPS workflow

kargo/infra/verification/prod-health-check.yaml

@@ -0,0 +1,37 @@
+apiVersion: argoproj.io/v1alpha1
+kind: AnalysisTemplate
+metadata:
+  name: prod-health-check
+  namespace: infra
+spec:
+  metrics:
+    - name: pod-health
+      successCondition: result == "healthy"
+      provider:
+        job:
+          spec:
+            template:
+              spec:
+                serviceAccountName: kargo-verifier
+                containers:
+                  - name: check
+                    image: alpine/k8s:1.35.1
+                    command: [sh, -c]
+                    args:
+                      - |
+                        set -e
+                        echo "Checking pod health..."
+                        cm=$(kubectl get pods -n cert-manager --no-headers 2>/dev/null | grep -c Running || echo 0)
+                        echo "cert-manager running pods: $cm"
+                        ar=$(kubectl get pods -n argo-rollouts --no-headers 2>/dev/null | grep -c Running || echo 0)
+                        echo "argo-rollouts running pods: $ar"
+                        gt=$(kubectl get pods -n gitea --no-headers 2>/dev/null | grep -c Running || echo 0)
+                        echo "gitea running pods: $gt"
+                        if [ "$cm" -ge 1 ] && [ "$ar" -ge 1 ] && [ "$gt" -ge 1 ]; then
+                          echo "healthy"
+                        else
+                          echo "unhealthy"
+                          exit 1
+                        fi
+                restartPolicy: Never
+            backoffLimit: 2