feat: add user search functionality

- Implemented `GET /users/search` endpoint in the backend to enable user search by username or display name.
- Added `search` method in `UsersService` and `UsersRepository`.
- Updated frontend `UserService` to support the new search API.

backend/src/users/users.controller.ts

@@ -54,6 +54,12 @@ export class UsersController {
 		return this.usersService.findPublicProfile(username);
 	}
 
+	@Get("search")
+	@UseGuards(AuthGuard)
+	search(@Query("q") query: string) {
+		return this.usersService.search(query);
+	}
+
 	// Gestion de son propre compte
 	@Get("me")
 	@UseGuards(AuthGuard)