feat(fullstack): Add notifications, user is now an entity, add testcontainers, rework custom permissions, get user from JWT in endpoints

legalconsenthub-backend/src/main/kotlin/com/betriebsratkanzlei/legalconsenthub/user/UserService.kt

@@ -0,0 +1,46 @@
+package com.betriebsratkanzlei.legalconsenthub.user
+
+import com.betriebsratkanzlei.legalconsenthub.error.UserAlreadyExistsException
+import com.betriebsratkanzlei.legalconsenthub.error.UserNotFoundException
+import com.betriebsratkanzlei.legalconsenthub.security.CustomJwtTokenPrincipal
+import com.betriebsratkanzlei.legalconsenthub_api.model.CreateUserDto
+import com.betriebsratkanzlei.legalconsenthub_api.model.UserStatus
+import org.springframework.security.core.context.SecurityContextHolder
+import org.springframework.stereotype.Service
+
+@Service
+class UserService(
+    private val userRepository: UserRepository
+) {
+
+    fun getCurrentUser(): User {
+        val principal = SecurityContextHolder.getContext().authentication.principal as CustomJwtTokenPrincipal
+        val userId = principal.id ?: throw IllegalStateException("User ID not found")
+
+        return userRepository.findById(userId)
+            .orElseThrow { UserNotFoundException(userId) }
+    }
+
+    fun createUser(createUserDto: CreateUserDto): User {
+        if (userRepository.existsById(createUserDto.id)) {
+            throw UserAlreadyExistsException(createUserDto.id)
+        }
+
+        val user = User(
+            id = createUserDto.id,
+            name = createUserDto.name,
+            status = createUserDto.status ?: UserStatus.ACTIVE,
+            role = createUserDto.role
+        )
+        return userRepository.save(user)
+    }
+
+    fun getUserById(userId: String): User {
+        return userRepository.findById(userId)
+            .orElseThrow { UserNotFoundException(userId) }
+    }
+
+    fun deleteUser(userId: String) {
+        userRepository.deleteById(userId)
+    }
+}