Add Garage S3-compatible object store to platform

Cluster-local object store for build artifacts (CLI binaries etc.)
so Docker builds don't depend on flaky external downloads.

- Single-node Garage v1.0.1 StatefulSet (LMDB, replication=1)
- Metadata on longhorn-nvme (1Gi), data on longhorn HDD (20Gi)
- S3 API at garage.platform.svc:3900
- External ingress at s3.coreworlds.io (internal-only)
- SealedSecret for admin token and RPC secret

infra/kubernetes/platform/traefik/certificate-internal.yaml

@@ -62,3 +62,16 @@ spec:
     kind: ClusterIssuer
   dnsNames:
     - gitea.coreworlds.io
+---
+apiVersion: cert-manager.io/v1
+kind: Certificate
+metadata:
+  name: garage-s3-tls
+  namespace: platform
+spec:
+  secretName: garage-s3-tls
+  issuerRef:
+    name: letsencrypt-production
+    kind: ClusterIssuer
+  dnsNames:
+    - s3.coreworlds.io