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/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();
+  }
+}