feat(render+admin): exports management (all users' rendered videos)

- render-svc: admin-scoped store (ListAllExports / GetExportByIDAny /
  SoftDeleteExportAny) + GET/DELETE/download-url under /v1/admin-exports
  (admin-gated; separate prefix so it routes to render, not identity's /admin)
- gateway: /v1/admin-exports/* → render
- admin /admin/exports: paginated table of every rendered export with thumbnail,
  type/quality, size, duration, dimensions, produce + expiry dates; download
  (presigned URL) and delete

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

services/render/cmd/server/main.go

@@ -145,6 +145,14 @@ func main() {
 		nodeFonts.DELETE("/:id", fontH.Delete)
 	}
 
+	// ── Exports management (admin: all users' rendered videos) ────────────────
+	adminExports := v1.Group("/admin-exports", auth, admin)
+	{
+		adminExports.GET("", exportH.AdminList)
+		adminExports.DELETE("/:export_id", exportH.AdminDelete)
+		adminExports.GET("/:export_id/download-url", exportH.AdminDownloadURL)
+	}
+
 	// ── Internal (node agents only — HMAC auth) ───────────────────────────────
 	internal := v1.Group("/internal", nodeAuth)
 	{