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/project/Project.java

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+package com.example.app.project;
+
+import jakarta.persistence.*;
+import lombok.Getter;
+import lombok.NoArgsConstructor;
+import lombok.Setter;
+
+@Entity
+@Table(name = "projects")
+@Getter
+@Setter
+@NoArgsConstructor
+public class Project {
+
+  @Id
+  @GeneratedValue(strategy = GenerationType.IDENTITY)
+  private Long id;
+
+  @Column(nullable = false)
+  private String name;
+
+  @Column(nullable = false)
+  private int timeBudgetMinutes;
+
+  @Column(nullable = false)
+  private int costBudgetCents;
+
+  /** Null means fall back to the logging user's defaultHourlyRateCents. */
+  @Column private Integer hourlyRateCents;
+}

backend/src/main/java/com/example/app/project/ProjectController.java

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+package com.example.app.project;
+
+import com.example.app.project.ProjectDtos.CreateProjectRequest;
+import com.example.app.project.ProjectDtos.ProjectResponse;
+import jakarta.validation.Valid;
+import java.util.List;
+import org.springframework.http.HttpStatus;
+import org.springframework.web.bind.annotation.*;
+
+@RestController
+@RequestMapping("/api/projects")
+public class ProjectController {
+
+  private final ProjectService projectService;
+
+  public ProjectController(ProjectService projectService) {
+    this.projectService = projectService;
+  }
+
+  @GetMapping
+  public List<ProjectResponse> list() {
+    return projectService.findAll();
+  }
+
+  @PostMapping
+  @ResponseStatus(HttpStatus.CREATED)
+  public ProjectResponse create(@Valid @RequestBody CreateProjectRequest req) {
+    return projectService.create(req);
+  }
+}

backend/src/main/java/com/example/app/project/ProjectDtos.java

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+package com.example.app.project;
+
+import jakarta.validation.constraints.Min;
+import jakarta.validation.constraints.NotBlank;
+import jakarta.validation.constraints.PositiveOrZero;
+
+public class ProjectDtos {
+
+  public record CreateProjectRequest(
+      @NotBlank String name,
+      @Min(1) int timeBudgetMinutes,
+      @PositiveOrZero int costBudgetCents,
+      @PositiveOrZero Integer hourlyRateCents) {}
+
+  public record ProjectResponse(
+      Long id,
+      String name,
+      int timeBudgetMinutes,
+      int costBudgetCents,
+      Integer hourlyRateCents,
+      long minutesLogged,
+      long costLoggedCents,
+      boolean timeExceeded,
+      boolean costExceeded) {
+
+    public static ProjectResponse from(Project p, long minutesLogged, long costLoggedCents) {
+      return new ProjectResponse(
+          p.getId(),
+          p.getName(),
+          p.getTimeBudgetMinutes(),
+          p.getCostBudgetCents(),
+          p.getHourlyRateCents(),
+          minutesLogged,
+          costLoggedCents,
+          minutesLogged > p.getTimeBudgetMinutes(),
+          costLoggedCents > p.getCostBudgetCents());
+    }
+  }
+}

backend/src/main/java/com/example/app/project/ProjectRepository.java

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+package com.example.app.project;
+
+import org.springframework.data.jpa.repository.JpaRepository;
+
+public interface ProjectRepository extends JpaRepository<Project, Long> {}

backend/src/main/java/com/example/app/project/ProjectService.java

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+package com.example.app.project;
+
+import com.example.app.project.ProjectDtos.CreateProjectRequest;
+import com.example.app.project.ProjectDtos.ProjectResponse;
+import com.example.app.time.TimeEntryRepository;
+import java.util.HashMap;
+import java.util.List;
+import java.util.Map;
+import org.springframework.stereotype.Service;
+import org.springframework.transaction.annotation.Transactional;
+
+@Service
+public class ProjectService {
+
+  private final ProjectRepository projectRepository;
+  private final TimeEntryRepository timeEntryRepository;
+
+  public ProjectService(
+      ProjectRepository projectRepository, TimeEntryRepository timeEntryRepository) {
+    this.projectRepository = projectRepository;
+    this.timeEntryRepository = timeEntryRepository;
+  }
+
+  @Transactional(readOnly = true)
+  public List<ProjectResponse> findAll() {
+    List<Project> projects = projectRepository.findAll();
+
+    // one aggregate query for totals across all entries
+    Map<Long, long[]> totals = new HashMap<>();
+    for (Object[] row : timeEntryRepository.aggregateAllByProject()) {
+      long projectId = ((Number) row[0]).longValue();
+      long minutes = ((Number) row[1]).longValue();
+      long cost = ((Number) row[2]).longValue();
+      totals.put(projectId, new long[] {minutes, cost});
+    }
+
+    return projects.stream()
+        .map(
+            p -> {
+              long[] t = totals.getOrDefault(p.getId(), new long[] {0, 0});
+              return ProjectResponse.from(p, t[0], t[1]);
+            })
+        .toList();
+  }
+
+  @Transactional
+  public ProjectResponse create(CreateProjectRequest req) {
+    Project p = new Project();
+    p.setName(req.name());
+    p.setTimeBudgetMinutes(req.timeBudgetMinutes());
+    p.setCostBudgetCents(req.costBudgetCents());
+    p.setHourlyRateCents(req.hourlyRateCents());
+    Project saved = projectRepository.save(p);
+    return ProjectResponse.from(saved, 0, 0);
+  }
+}