feat: implement User Delete API / ユーザー削除APIの実装

[zigzagdev]

Motivation / 目的

Implement the User Delete API (DELETE /api/v1/users/{id}) across all layers as part of #514.

ユーザー削除API（DELETE /api/v1/users/{id}）をInfra・Application・Presentation層にわたって実装しました（#514）。

What I have done / 実施内容

Infra層 (PR #521)

• UserRepositroyInterface: deleteUser(int $id): void を追加
• UserRepository: deleteUser 実装
  • IDでユーザーを検索し、存在しない場合は Exception('User not found.') をスロー
  • delete() でレコードを削除
• UserRepositoryTest: DBインテグレーションテストを2件追加

Application層 (PR #522)

• DeleteUserUseCase: handle(int $id): void
  • Command オブジェクト不要（削除に必要なのは ID のみ）
  • UserRepositroyInterface::deleteUser() を呼び出し、例外はリポジトリから自動伝播

Presentation層 (PR #523)

• UserController::deleteUser(): route {id} を int にキャストして DeleteUserUseCase を呼び出す
  • 200 on success
  • 404 when 'User not found.' exception is thrown
  • 500 on other errors with Log::error
• Route: DELETE /api/v1/users/{id}

Test Results / テスト結果

Infra層

• test_deleteUser_removes_user_when_exists
• test_deleteUser_throws_exception_when_user_not_found

Application層

• test_handle_calls_repository_deleteUser_with_given_id
• test_handle_propagates_exception_when_user_not_found

Presentation層

• test_delete_user_returns_200_when_user_exists
• test_delete_user_returns_404_when_user_not_found

Closes #514

[codecov]

Codecov Report

❌ Patch coverage is 91.01124% with 8 lines in your changes missing coverage. Please review.
✅ Project coverage is 60.30%. Comparing base (07483b1) to head (8836cc7).

Files with missing lines	Patch %	Lines
...pp/Packages/Features/Controller/UserController.php	57.89%	8 Missing ⚠️

Additional details and impacted files

@@               Coverage Diff               @@
##             feat/user     #524      +/-   ##
===============================================
+ Coverage        59.94%   60.30%   +0.35%     
- Complexity        1515     1534      +19     
===============================================
  Files              120      123       +3     
  Lines             7765     7854      +89     
===============================================
+ Hits              4655     4736      +81     
- Misses            3110     3118       +8     

Files with missing lines	Coverage Δ
.../app/Packages/Domains/Tests/UserRepositoryTest.php	100.00% <100.00%> (ø)
src/app/Packages/Domains/UserRepository.php	97.43% <100.00%> (+0.37%)	⬆️
...CommandUseCases/UseCase/User/DeleteUserUseCase.php	100.00% <100.00%> (ø)
...es/Tests/CommandUseCases/DeleteUserUseCaseTest.php	100.00% <100.00%> (ø)
src/app/Packages/Features/Tests/DeleteUserTest.php	100.00% <100.00%> (ø)
...pp/Packages/Features/Controller/UserController.php	79.74% <57.89%> (-6.92%)	⬇️

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