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/app.module.ts

@@ -8,6 +8,7 @@ import { ForcePasswordChangeInterceptor } from './auth/interceptors/force-passwo
 import { HealthModule } from './health/health.module';
 import { LdapModule } from './ldap/ldap.module';
 import { MailModule } from './mail/mail.module';
+import { DashboardModule } from './dashboard/dashboard.module';
 import { DomaincheckModule } from './domaincheck/domaincheck.module';
 import { ModuleRegistryModule } from './module-registry/module-registry.module';
 import { PrismaModule } from './prisma/prisma.module';
@@ -27,6 +28,7 @@ import { UserModule } from './user/user.module';
     LdapModule,
     ModuleRegistryModule,
     DomaincheckModule,
+    DashboardModule,
   ],
   providers: [
     // Global JWT guard: all routes require auth unless @Public()