feat(studio): copy template scene graph into editable project (use-template works)

Build now created an EMPTY project: (1) the studio binds camelCase but the frontend
sent snake_case → original_project_id dropped to Guid.Empty; (2) CreateProjectAsync
never copied scenes. Now:
- saved-projects.ts sends camelCase (originalProjectId/copyDefaultValues).
- /api/projects resolves the container slug → first published variant content project.
- StudioService.CreateProjectAsync deep-copies the content scene graph (scenes +
  content elements + scene colours + shared colours) into the new saved project via
  one atomic cross-schema SQL copy (enum cols cast to text; temp scene-id map).

Verified: insta-promo → 1 scene, 6 content fields, 4 shared colours, loadable by the
studio editor.

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

services/studio/FlatRender.StudioSvc/Application/Services/StudioService.cs

@@ -81,11 +81,84 @@ public class StudioService(StudioDbContext db)
             ProjectDurationSec = 0,
         };
 
+        await using var tx = await db.Database.BeginTransactionAsync();
         db.SavedProjects.Add(project);
         await db.SaveChangesAsync();
+
+        // Deep-copy the template's scene graph (scenes + content/colour elements) from
+        // the content schema so the new project opens editable in the studio. Same DB,
+        // so this is one atomic cross-schema copy.
+        if (req.CopyDefaultValues && req.OriginalProjectId != Guid.Empty)
+            await CopyTemplateGraphAsync(project.Id, req.OriginalProjectId);
+
+        await tx.CommitAsync();
         return await GetProjectAsync(project.Id, userId);
     }
 
+    /// <summary>
+    /// Copies a content template project's scenes, content elements and colour elements
+    /// into a freshly-created editable project. Runs inside the caller's transaction;
+    /// the temp scene-id map drops on commit. Same Postgres DB → atomic cross-schema copy.
+    /// </summary>
+    private async Task CopyTemplateGraphAsync(Guid savedProjectId, Guid originalProjectId)
+    {
+        // 1. scenes → capture old→new id mapping in a temp table
+        await db.Database.ExecuteSqlRawAsync(@"
+            CREATE TEMP TABLE _scene_map ON COMMIT DROP AS
+            WITH ins AS (
+                INSERT INTO studio.saved_scenes
+                    (saved_project_id, original_scene_id, key, title, image, demo,
+                     scene_color_svg, scene_type, sort, scene_length_sec, min_duration_sec,
+                     max_duration_sec, overlap_at_end_sec, can_handle_duration,
+                     manual_color_selection, created_at, updated_at)
+                SELECT {0}, s.id, s.key, s.title, s.image, s.demo, s.scene_color_svg,
+                       s.scene_type::text, s.sort, COALESCE(s.default_duration_sec, 0),
+                       s.min_duration_sec, s.max_duration_sec, s.overlap_at_end_sec,
+                       s.can_handle_duration, s.manual_color_selection, now(), now()
+                FROM content.scenes s
+                WHERE s.project_id = {1} AND s.deleted_at IS NULL AND s.is_active = true
+                RETURNING id AS new_id, original_scene_id AS old_id
+            )
+            SELECT new_id, old_id FROM ins;",
+            savedProjectId, originalProjectId);
+
+        // 2. content elements (skip repeater children for now)
+        await db.Database.ExecuteSqlRawAsync(@"
+            INSERT INTO studio.saved_scene_contents
+                (saved_scene_id, key, title, localized_title, hint, type, value,
+                 font_face, font_face_name, font_size, default_font_size, default_font_face,
+                 justify, position_in_container, direction_layer_value, is_text_box,
+                 ai_input_type, mapped_list, thumbnail, sort, status, created_at, updated_at)
+            SELECT sm.new_id, ce.key, ce.title, ce.localized_title, ce.hint, ce.type::text,
+                   ce.default_value, ce.font_face, ce.font_face_name, ce.font_size,
+                   ce.default_font_size, ce.default_font_face, ce.justify::text,
+                   ce.position_in_container, ce.direction_layer_value, ce.is_text_box,
+                   ce.ai_input_type::text, ce.mapped_list, ce.thumbnail, ce.sort, 'default',
+                   now(), now()
+            FROM content.scene_content_elements ce
+            JOIN _scene_map sm ON sm.old_id = ce.scene_id
+            WHERE ce.repeater_item_id IS NULL;");
+
+        // 3. colour elements
+        await db.Database.ExecuteSqlRawAsync(@"
+            INSERT INTO studio.saved_scene_colors
+                (saved_scene_id, element_key, title, icon, attr_value, value, is_selected, sort)
+            SELECT sm.new_id, ce.element_key, ce.title, ce.icon, ce.attr_value::text,
+                   COALESCE(ce.default_color, ''), false, ce.sort
+            FROM content.scene_color_elements ce
+            JOIN _scene_map sm ON sm.old_id = ce.scene_id;");
+
+        // 4. shared (project-level) colours — frshare frd_* controls
+        await db.Database.ExecuteSqlRawAsync(@"
+            INSERT INTO studio.saved_shared_colors
+                (saved_project_id, element_key, title, icon, attr_value, value, is_selected, sort)
+            SELECT {0}, sc.element_key, sc.title, sc.icon, sc.attr_value::text,
+                   COALESCE(sc.default_color, ''), false, sc.sort
+            FROM content.shared_colors sc
+            WHERE sc.project_id = {1};",
+            savedProjectId, originalProjectId);
+    }
+
     public async Task<SavedProjectFullResponse> UpdateProjectAsync(
         Guid id, Guid userId, UpdateSavedProjectRequest req)
     {