feat(admin): discount edit/delete + project-scoped scene/color editor

Identity (discounts):
- DiscountsController: PUT /v1/discounts/{id}, DELETE /v1/discounts/{id}
- DiscountService.UpdateAsync (partial update, code-clash guard) + DeleteAsync
- UpdateDiscountRequest record (all fields optional incl. is_active)
- Frontend discountsConfig: canEdit + canDelete + is_active field

Content (scenes/colors — UI for existing CRUD endpoints):
- New SceneColorEditor.tsx: 3-tab modal (scenes / shared-colors / color-presets),
  project-scoped, full add/edit/delete per tab, colour pickers + palette item editor
- Wired into TemplatesAdmin: "صحنه‌ها و رنگ‌ها" button per template variant row
- Routes through the generic admin proxy with ?project_id=

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

services/identity/FlatRender.IdentitySvc/Application/Services/Interfaces/IDiscountService.cs

@@ -8,4 +8,6 @@ public interface IDiscountService
     Task<DiscountValidateResponse> ValidateAsync(Guid tenantId, string code, Guid? planId);
     Task<PagedResponse<DiscountResponse>> ListAsync(Guid tenantId, int page, int pageSize);
     Task<DiscountResponse> CreateAsync(Guid tenantId, CreateDiscountRequest request);
+    Task<DiscountResponse?> UpdateAsync(Guid tenantId, Guid id, UpdateDiscountRequest request);
+    Task<bool> DeleteAsync(Guid tenantId, Guid id);
 }