Restructure the book to the 3rd-edition layout (OUTLINE.md + content moves)

[schacon]

Summary

Three things on this branch:

1. OUTLINE.md — the canonical punch list for the 3rd edition: one table row per section (Section, Title, Description, Effort, Status), per-chapter source-file notes, the dropped-content survivor map, open decisions, and cross-cutting mechanical tasks.
2. The restructure itself — book/ now matches that layout. No book prose was written or rewritten; this is moves, renames, placeholders, and cross-reference plumbing.
3. Cross-reference rendering fix — links no longer render as raw filenames.

New chapter map

Getting Started · Git Basics · Git Branching · Distributed Git (ch04, was ch05) · Git Toolkit (ch05, was ch07 "Git Tools") · Customizing Git (ch06, was ch08) · Git and Agents (ch07, new) · Git Servers (ch08, was ch04 "Git on the Server") · Git at Scale (ch09, new) · Git Internals (ch10) · Appendix A: Git Commands (was Appendix C)

Dropped: the GitHub chapter (ch06/), Git and Other Systems (ch09/), Appendix A (environments), Appendix B (embedding), plus 68 images referenced only by those chapters.

What was added

• Placeholder chapters in the preface's outline-notes style: ch07-git-and-agents.asc (5 sections) and ch09-git-at-scale.asc (7 sections), each with AUTHOR TODO markers so humans write the prose.
• Placeholder sections: ch03/worktrees.asc (3.5), ch04/pull-requests.asc (4.3), ch06/ignoring.asc (6.2).
• The 4.3 placeholder carries the rescued anchors from the dropped GitHub chapter (_pr_refs, _fetch_and_push_on_different_repositories, _email_notifications), so every existing cross-reference still resolves.

Cross-reference handling

• All xrefs retargeted to the new chapter names; appendix entries pointing at the dropped Other Systems chapter commented out with AUTHOR TODO notes; prose made inaccurate by the reordering flagged with AUTHOR TODO comments for human rewriting.
• Link rendering fix: all 218 inter-document xrefs (<<chXX-file#anchor>>) converted to internal xrefs with explicit link text (<<anchor,Ch N, Title>>). Asciidoctor rendered the old form as a dead inter-document link whose visible text was the raw filename ("ch01-getting-started.html"); the book builds as a single document, so the internal form is correct in every output format, and the reader's link rewriter now maps them to the right section pages automatically. Anchors verified unique book-wide.

Verification

• HTML/EPUB/FB2/PDF all build with no warnings; all 213 internal links in the generated HTML resolve (scripted check; the only remaining .html hrefs are four external URLs).
• Reader demo of the new structure:

• Cross-references now render as chapter labels and navigate correctly:

  

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