feat: INSTALL.md is the English installation tutorial; new tutorial docs/tutorials/first-source-to-first-answer.md with a shipped sample source; README.md links it as its first-ingestion step (#191)

Files changed:
- CHANGES.md
- INSTALL.md
- README.md
- VERSION
- docs/reference/commands/types-instructions-and-docs.md
- docs/tutorials/README.md
- docs/tutorials/first-source-to-first-answer.md
- docs/tutorials/sample-source.md
- instructions/dev/doc-pull-through.md
- tools/CONTRACT.md
- tools/chemenu/commands/docs_verify.py
- tools/chemenu/install_doc.py
- tools/chemenu/tests/test_install_doc.py

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

VERSION

@@ -1 +1 @@
-9.0.0-beta.6
+9.0.0-beta.7