feat: add user_favorite migration for favorite heritages join table

[zigzagdev]

Summary

• ユーザーがお気に入り登録した世界遺産を管理するための user_favorite 中間テーブルを追加
• users / world_heritage_sites への外部キー制約（cascadeOnDelete）を設定
• user_id + world_heritage_site_id の複合ユニーク制約により、同一ユーザー・同一遺産の重複登録を防止

Changes

• database/migrations/2026_08_01_000000_create_user_favorite_table.php を追加
• .gitignore に src/.config/（psyshのローカルキャッシュ）を追加

Test plan

• php artisan migrate でマイグレーションが正常に実行されることを確認
• php artisan migrate:rollback でロールバックできることを確認

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 62.90%. Comparing base (9c6c1d1) to head (66cd289).

Additional details and impacted files

@@                  Coverage Diff                  @@
##             feat/user-favorite     #560   +/-   ##
=====================================================
  Coverage                 62.90%   62.90%           
  Complexity                 1622     1622           
=====================================================
  Files                       136      136           
  Lines                      8410     8410           
=====================================================
  Hits                       5290     5290           
  Misses                     3120     3120           

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[zigzagdev]

OK