fix: Wrap admin subscriptions response to match frontend contract

Frontend expects { subscriptions: [{ owner_email, module_name, license_id }] }
but backend returned raw WebstoreSubscription entities. Shaped the response
with license.owner join for owner_email and plan_id mapped to module_name.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

backend-nest/src/modules/admin/admin.service.ts

@@ -151,10 +151,18 @@ export class AdminService {
   }
 
   async getSubscriptions() {
-    return this.webstoreSubRepo.find({
-      relations: ['license'],
+    const subs = await this.webstoreSubRepo.find({
+      relations: ['license', 'license.owner'],
       order: { created_at: 'DESC' },
     });
+
+    return {
+      subscriptions: subs.map(sub => ({
+        owner_email: sub.license?.owner?.email ?? 'Unknown',
+        module_name: sub.plan_id,
+        license_id: sub.license_id,
+      })),
+    };
   }
 
   async getServers() {