1.0.1

feat(locale): Japanese (ja) translation; 1.0.1

• Lang/ja mirrors Lang/en (same keys and placeholders).
• README in Japanese (readme_ja.md / README_ja.md) and a three-language bar
  (Tiếng Việt · English · 日本語) on every README; version bumped to 1.0.1.

Co-Authored-By: Claude Opus 5.5 noreply@anthropic.com