feat(05-01): dashboard backend — Prisma models, CRUD API, module wiring

- Add DashboardLayout and WidgetInstance Prisma models with userId/tenantId scoping
- Create DashboardController with 6 endpoints (layout CRUD + widget CRUD)
- Create DashboardService with ownership verification on all widget mutations (T-05-01)
- Add SaveLayoutDto, CreateWidgetDto, UpdateWidgetConfigDto with class-validator
- Register DashboardModule in app.module.ts imports

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

apps/api/src/dashboard/dashboard.module.ts

@@ -0,0 +1,19 @@
+import { Module } from '@nestjs/common';
+import { DashboardController } from './dashboard.controller';
+import { DashboardService } from './dashboard.service';
+
+/**
+ * NestJS module for dashboard layout and widget management.
+ *
+ * Provides:
+ * - DashboardService: CRUD for per-user dashboard layouts and widget instances
+ * - DashboardController: REST API for layout and widget operations
+ *
+ * Exports DashboardService so downstream modules can access layout/widget data.
+ */
+@Module({
+  controllers: [DashboardController],
+  providers: [DashboardService],
+  exports: [DashboardService],
+})
+export class DashboardModule {}