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

VERSION

@@ -1 +1 @@
-8.0.0-beta.20
+8.0.0-beta.21