feat(templates): remote template registry via CONTAINR_TEMPLATE_REGISTRY_URL (#52)

- GET /templates merges a remote Containr catalog as source:"registry"
  (5s timeout, 60s cache, offline-safe)
- GET /templates/:id falls through to the registry
- Deploy of a registry template materializes a deterministic private
  copy for the deployer — repeat deploys reuse it
- Templates page badges registry entries; openapi + env documented

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Co-authored-by: Devin <158243242+devin-ai-integration[bot]@users.noreply.github.com>

app/frontend/src/lib/api-client.ts

@@ -181,6 +181,7 @@ export type TemplateEntity = {
   isOfficial: boolean;
   ownerId: string | null;
   isPublic: boolean;
+  source?: string;
   createdAt?: string;
   updatedAt?: string;
 };
@@ -751,6 +752,7 @@ function normalizeTemplate(template: RawServiceTemplate): TemplateEntity | null
     isOfficial: Boolean(template.is_official),
     ownerId: template.owner_id ?? null,
     isPublic: Boolean(template.is_public),
+    source: template.source,
     createdAt: template.created_at,
     updatedAt: template.updated_at,
   };