feat: add dynamic files to gitignore

Add multi-language system dynamic files to .gitignore:
- CLAUDE.md (generated by npm run lang:ja/en)
- docs/rules/ (generated from language-specific sources)
- docs/guides/sub-agents.md (generated from language-specific sources)
- .claude/commands/ (generated from language-specific sources)
- .claude/agents/ (generated from language-specific sources)
- .claudelang (language configuration file)

These files are now properly excluded from git and will be generated on-demand by npm scripts.

🤖 Generated with [Claude Code](https://claude.ai/code)

Co-Authored-By: Claude <noreply@anthropic.com>

Author: shinpr

.gitignore

@@ -48,4 +48,12 @@ docs/plans/*
 # 作業計画書タスク（自動生成）
 docs/plans/tasks/
 
+# 多言語化関連（npm scriptsで動的生成）
+.claudelang
+CLAUDE.md
+docs/rules/
+docs/guides/sub-agents.md
+.claude/commands/
+.claude/agents/
+