feat(backend): implement domain — users, projects, time entries, reports

- User, Project, TimeEntry JPA entities with SLF4J logging in services
- Native SQL aggregate queries: per-day (weekly) and per-project (monthly)
  both using COALESCE(project_rate, user_rate) for cost calculation
- ReportService parses ISO week/month strings, fills zero-day gaps,
  computes timeBudgetPct / costBudgetPct / breached per project
- ProjectService piggybacks on aggregateAllByProject for budget status
  on GET /api/projects (no N+1)
- GlobalExceptionHandler maps validation errors → 400 ProblemDetail,
  EntityNotFoundException → 404, IllegalArgumentException → 400
- Lombok on pom.xml (optional, used for @Getter/@Setter/@NoArgsConstructor)

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

backend/src/main/java/com/example/app/user/User.java

@@ -0,0 +1,24 @@
+package com.example.app.user;
+
+import jakarta.persistence.*;
+import lombok.Getter;
+import lombok.NoArgsConstructor;
+import lombok.Setter;
+
+@Entity
+@Table(name = "users")
+@Getter
+@Setter
+@NoArgsConstructor
+public class User {
+
+  @Id
+  @GeneratedValue(strategy = GenerationType.IDENTITY)
+  private Long id;
+
+  @Column(nullable = false)
+  private String name;
+
+  @Column(nullable = false)
+  private int defaultHourlyRateCents;
+}

backend/src/main/java/com/example/app/user/UserController.java

@@ -0,0 +1,23 @@
+package com.example.app.user;
+
+import com.example.app.user.UserDtos.UserResponse;
+import java.util.List;
+import org.springframework.web.bind.annotation.GetMapping;
+import org.springframework.web.bind.annotation.RequestMapping;
+import org.springframework.web.bind.annotation.RestController;
+
+@RestController
+@RequestMapping("/api/users")
+public class UserController {
+
+  private final UserService userService;
+
+  public UserController(UserService userService) {
+    this.userService = userService;
+  }
+
+  @GetMapping
+  public List<UserResponse> list() {
+    return userService.findAll();
+  }
+}

backend/src/main/java/com/example/app/user/UserDtos.java

@@ -0,0 +1,11 @@
+package com.example.app.user;
+
+public class UserDtos {
+
+  public record UserResponse(Long id, String name, int defaultHourlyRateCents) {
+
+    public static UserResponse from(User user) {
+      return new UserResponse(user.getId(), user.getName(), user.getDefaultHourlyRateCents());
+    }
+  }
+}

backend/src/main/java/com/example/app/user/UserRepository.java

@@ -0,0 +1,5 @@
+package com.example.app.user;
+
+import org.springframework.data.jpa.repository.JpaRepository;
+
+public interface UserRepository extends JpaRepository<User, Long> {}

backend/src/main/java/com/example/app/user/UserService.java

@@ -0,0 +1,21 @@
+package com.example.app.user;
+
+import com.example.app.user.UserDtos.UserResponse;
+import java.util.List;
+import org.springframework.stereotype.Service;
+import org.springframework.transaction.annotation.Transactional;
+
+@Service
+@Transactional(readOnly = true)
+public class UserService {
+
+  private final UserRepository userRepository;
+
+  public UserService(UserRepository userRepository) {
+    this.userRepository = userRepository;
+  }
+
+  public List<UserResponse> findAll() {
+    return userRepository.findAll().stream().map(UserResponse::from).toList();
+  }
+}