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

infra/traefik-routes/manifests/tls-store.yaml

@@ -0,0 +1,10 @@
+# Default TLS store — uses wildcard-tls from kube-system as default cert.
+# All IngressRoutes with tls: {} will use this certificate.
+apiVersion: traefik.io/v1alpha1
+kind: TLSStore
+metadata:
+  name: default
+  namespace: kube-system
+spec:
+  defaultCertificate:
+    secretName: wildcard-tls