feat(03-01): add ModuleRegistry NestJS module with CRUD and activation endpoints

- ModuleRegistryService with findAll, findBySlug, findActiveForTenant, activate/deactivate, seedModule
- ModuleRegistryController with GET /modules, GET /modules/active, POST activate/deactivate
- ModuleGuard + @UseModule() decorator for tenant-scoped module access control
- ActivateModuleDto with UUID validation
- Registered ModuleRegistryModule in AppModule imports

apps/api/src/module-registry/dto/activate-module.dto.ts

@@ -0,0 +1,6 @@
+import { IsUUID } from 'class-validator';
+
+export class ActivateModuleDto {
+  @IsUUID()
+  moduleId!: string;
+}