fix: corrected repository to accurately reflect UUID as ID

Author: stark-cybertech

server/user/src/main/java/meet_at_mensa/user/UserRepository.java

@@ -2,10 +2,13 @@
 
 // import CRUD repository (Create/Read/Update/Delete)
 import org.springframework.data.repository.CrudRepository;
+import java.util.UUID;
 
 // Interface UserRepository represents the userdb table
-public interface UserRepository extends CrudRepository<User, Integer> {
+public interface UserRepository extends CrudRepository<User, UUID> {
 
     // This is auto-implemented by springboot into a userRepository Bean
 
+    // We only ever need to get users by the UUID, so no further functions need to be defined here
+
 }