✨ feat(admin): add user data dashboard for cross-project data visualization

Add comprehensive admin dashboard to view and manage user data across all projects:

Backend:
- Add admin endpoints to Chat, Todo, Contacts, Calendar, Picture, Zitare, Presi
- Each backend exposes GET/DELETE /api/v1/admin/user-data/:userId
- Service-to-service auth via X-Service-Key header

Aggregation (mana-core-auth):
- GET /api/v1/admin/users - Paginated user list with search
- GET /api/v1/admin/users/:userId/data - Aggregated data from all backends
- DELETE /api/v1/admin/users/:userId/data - GDPR deletion across all projects

Frontend (ManaCore web):
- New User Data tab in admin navigation
- User search page at /admin/user-data
- User detail page with ProjectDataCard components
- GDPR deletion dialog with email confirmation

Presi:
- Migrate user_id from UUID to TEXT for Better Auth compatibility
- Add SQL migration script

services/mana-core-auth/src/admin/user-data.controller.ts

@@ -0,0 +1,66 @@
+import {
+	Controller,
+	Get,
+	Delete,
+	Param,
+	Query,
+	UseGuards,
+	Logger,
+	HttpCode,
+	HttpStatus,
+} from '@nestjs/common';
+import { UserDataService } from './user-data.service';
+import { AdminGuard } from './guards/admin.guard';
+import { UserDataSummary, DeleteUserDataResponse, UserListResponse } from './dto/user-data.dto';
+
+/**
+ * Admin controller for cross-project user data management
+ * All endpoints require admin authentication (role=admin or in ADMIN_USER_IDS)
+ */
+@Controller('api/v1/admin')
+@UseGuards(AdminGuard)
+export class UserDataController {
+	private readonly logger = new Logger(UserDataController.name);
+
+	constructor(private readonly userDataService: UserDataService) {}
+
+	/**
+	 * List all users with pagination and search
+	 * GET /api/v1/admin/users?page=1&limit=20&search=email
+	 */
+	@Get('users')
+	async getUsers(
+		@Query('page') page?: string,
+		@Query('limit') limit?: string,
+		@Query('search') search?: string
+	): Promise<UserListResponse> {
+		const pageNum = parseInt(page || '1', 10);
+		const limitNum = Math.min(parseInt(limit || '20', 10), 100);
+
+		this.logger.log(
+			`Admin request: getUsers page=${pageNum} limit=${limitNum} search=${search || ''}`
+		);
+		return this.userDataService.getUsers(pageNum, limitNum, search);
+	}
+
+	/**
+	 * Get aggregated user data from all projects
+	 * GET /api/v1/admin/users/:userId/data
+	 */
+	@Get('users/:userId/data')
+	async getUserData(@Param('userId') userId: string): Promise<UserDataSummary> {
+		this.logger.log(`Admin request: getUserData for userId=${userId}`);
+		return this.userDataService.getUserDataSummary(userId);
+	}
+
+	/**
+	 * Delete all user data across all projects (GDPR right to be forgotten)
+	 * DELETE /api/v1/admin/users/:userId/data
+	 */
+	@Delete('users/:userId/data')
+	@HttpCode(HttpStatus.OK)
+	async deleteUserData(@Param('userId') userId: string): Promise<DeleteUserDataResponse> {
+		this.logger.log(`Admin request: deleteUserData for userId=${userId}`);
+		return this.userDataService.deleteUserData(userId);
+	}
+}