docs(ja-JP): translate plain text code blocks to Japanese

Translate English prose inside plain text code blocks (```text, ```)
across ja-JP documentation to Japanese, following the same approach
as PR #753 (zh-CN translation).

Translated content includes:
- Output template labels and status messages
- Folder tree inline comments
- CLI workflow descriptions
- Error/warning message examples
- Commit message templates and PR title examples

Technical identifiers, file paths, and actual code remain untranslated.

docs/ja-JP/skills/golang-testing/SKILL.md

@@ -113,7 +113,7 @@ mypackage/
 ├── testdata/             # テストフィクスチャ
 │   ├── valid_user.json
 │   └── invalid_user.json
-└── export_test.go        # 内部のテストのための非公開のエクスポート
+└── export_test.go        # 内部テスト用の非公開エクスポート
 ```
 
 ### テストパッケージ