Issue #142 P2: 付録Aをswitch/restoreに統一

[ootakazuhiko]

Issue #142 の P2（付録Aのコマンドを推奨形へ）対応です。

変更点

• git checkout による「切替/復元」を、推奨形の git switch / git restore に整理（docs/src/appendix-git-commands-reference/index.md）
• 本文側（ブランチ操作の説明）も git switch に寄せて整合（docs/src/chapter-git-basics/index.md）

補足

• docs/src/chapter-docs-as-code/index.md の git checkout -b は、PR Issue #142 P1: Pages公開導線の整理 + AI利用ポリシー #145 側で git switch -c に統一済みです（先に Issue #142 P1: Pages公開導線の整理 + AI利用ポリシー #145 をマージすると全体として整合します）。

関連

• Issue: 改善提案 Issue 一覧（GitHub初心者ガイド / github-guide-for-beginners-book） #142

[Copilot]

Pull request overview

This PR modernizes Git command documentation by migrating from git checkout to the newer, more explicit git switch (for branch operations) and git restore (for file restoration) commands introduced in Git 2.23. This change improves clarity by separating branch switching from file restoration operations.

Changes:

• Updated branch operation examples in the Git basics chapter to use git switch and git switch -c
• Replaced file restoration examples in the appendix from git checkout -- to git restore with appropriate options
• Added explanatory notes in both files clarifying the transition from old to new command syntax

Reviewed changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated no comments.

File	Description
docs/src/chapter-git-basics/index.md	Updated branch creation and switching examples to use git switch instead of git checkout, added note explaining the modern command approach
docs/src/appendix-git-commands-reference/index.md	Replaced file restoration commands with git restore, updated branch switching commands to git switch, added explanatory notes, and updated the combined workflow example

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