fix(templates): real scene count on template pages (was always 0)

The card + detail read template.sceneCount, but the API never sent one — so the
frontend mapper hardcoded sceneCount:0 for every DB-backed template.

- content-svc: ContainerSummaryResponse + ContainerDetailResponse now carry
  SceneCount. The list computes it with one grouped query (scenes per aspect project,
  max across aspects); the detail loads scenes and counts them.
- frontend: V2ContainerSummary.scene_count → AdminProject.sceneCount → the catalog
  card/detail (adminProjectToCatalogTemplate no longer hardcodes 0).

Verified on the live local API: fr-instagram-promo → 5, single-scene templates → 1.

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

services/content/FlatRender.ContentSvc/Models/Responses/Responses.cs

@@ -82,7 +82,8 @@ public record ContainerSummaryResponse(
     int Sort,
     DateTime SortDate,
     List<string> CategorySlugs,
-    List<string> Tags
+    List<string> Tags,
+    int SceneCount
 );
 
 public record ContainerDetailResponse(
@@ -109,7 +110,8 @@ public record ContainerDetailResponse(
     DateTime SortDate,
     List<ProjectResponse> Projects,
     List<CategoryResponse> Categories,
-    List<TagResponse> Tags
+    List<TagResponse> Tags,
+    int SceneCount
 );
 
 public record ProjectResponse(