feat: INSTALL.md held to the installation instructions - prerequisites lists generated from the manifest, setup questions checked by docs verify (#154)

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01SnAJ7Z3CpVD3PRbN73QtU2

Files changed:
- CHANGES.md
- INSTALL.md
- VERSION
- instructions/dev/doc-pull-through.md
- instructions/dev/stack-close/SKILL.md
- instructions/setup-instance.md
- tools/CONTRACT.md
- tools/README.md
- tools/chemenu/cli_contract.py
- tools/chemenu/commands/docs_verify.py
- tools/chemenu/install_doc.py
- tools/chemenu/tests/test_install_doc.py

tools/README.md

@@ -85,6 +85,7 @@ tools/
     toolpaths.py           where git and rg are started from: .wikitool-tools.json, bare name only without the file
     filelock.py            an exclusive lock on an open file, flock on POSIX and msvcrt on Windows - the only module that imports either
     prerequisites.py       prerequisites.txt read from Python, plus the platform and long-path questions `doctor` asks
+    install_doc.py         INSTALL.md held to the instructions: its prerequisites lists generated from prerequisites.txt, its setup questions matched to setup-instance.md's markers
     corpus_cache.py        one parsed corpus per commit, never cached while the tree is dirty
     kb_scan.py             page iteration/loading over kb/
     blocks.py              generated regions in a page body, found by marker rather than by heading