fix: add missing newlines to MFA documentation files

- Add newline at end of MFA.md
- Add newline at end of web/docs/MFA_IMPLEMENTATION.md
- Add newline at end of web/docs/MFA_TESTING.md
- Fixes remaining Super-linter EditorConfig violations

MFA.md

@@ -198,4 +198,4 @@ CREATE TABLE account_mfa_settings (
 ---
 
 *Last updated: 2025-07-09*  
-*Implementation completed and tested successfully*
+*Implementation completed and tested successfully*

web/docs/MFA_IMPLEMENTATION.md

@@ -171,4 +171,4 @@ Accountテーブルに追加されたフィールド:
 ## 連絡先
 実装に関する質問がある場合は、このドキュメントと併せて以下を参照してください：
 - `/CLAUDE.md` - プロジェクト固有のルール
-- `/api/tests/mfa_test_instructions.md` - テスト手順詳細
+- `/api/tests/mfa_test_instructions.md` - テスト手順詳細

web/docs/MFA_TESTING.md

@@ -97,4 +97,4 @@ Based on the implementation, here are the key scenarios to test manually:
 1. Install test dependencies in Docker containers during build
 2. Add test commands to Makefile for easier execution
 3. Consider using Flask test client fixtures for better test isolation
-4. Add integration tests that test the full MFA flow end-to-end
+4. Add integration tests that test the full MFA flow end-to-end