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/generated/api-types.ts

@@ -11094,6 +11094,8 @@ export interface components {
             owner_id?: string | null;
             /** @description Whether a user-created template is published to the public catalog */
             is_public?: boolean;
+            /** @description Catalog origin: absent for local/official templates; "registry" for entries merged from CONTAINR_TEMPLATE_REGISTRY_URL. Deploying a registry template materializes a local copy first. */
+            source?: string;
             /**
              * Format: date-time
              * @description Creation timestamp