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.

frontend/src/services/user.service.ts

@@ -12,6 +12,13 @@ export const UserService = {
 		return data;
 	},
 
+	async search(query: string): Promise<User[]> {
+		const { data } = await api.get<User[]>("/users/search", {
+			params: { q: query },
+		});
+		return data;
+	},
+
 	async updateMe(update: Partial<User>): Promise<User> {
 		const { data } = await api.patch<User>("/users/me", update);
 		return data;