feat(raw): raw derive writes an Excel file's sheets as TSV files with a formula list (#202)

Each sheet becomes NN-<sheet>.tsv (RFC 4180, tab-delimited, A1-aligned) in a
<stem>.sheets/ folder beside the .md; sheets with formulas also get a
.formulas.tsv. derived.md is the overview. Adds testfiles/ with a CI test.

Files changed:
- .gitattributes
- CHANGES.md
- VERSION
- docs/dev/development.md
- docs/how-to/ingest-a-source.md
- docs/reference/commands/raw-material-and-uploads.md
- raw/CONTRACT.md
- testfiles/README.md
- tools/CONTRACT.md
- tools/chemenu/commands/raw_cmd.py
- tools/chemenu/filters/__init__.py
- tools/chemenu/filters/archive.py
- tools/chemenu/filters/ooxml.py
- tools/chemenu/tests/test_raw_derive.py
- tools/chemenu/tests/test_raw_derive_testfiles.py

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

docs/dev/development.md

@@ -40,6 +40,9 @@ Then have the agent run `instructions/bootstrap.md`: the preflight, then
 and how `dist export` runs as a test tool - is
 [instructions/dev/dev-setup.md](../../instructions/dev/dev-setup.md).
 
+Real documents for `raw derive` live in [testfiles/](../../testfiles/README.md) and are
+committed, so CI derives them too. The repository is public: that README says what may go in.
+
 What a clone has and an instance does not:
 
 - **The demo corpus.** Some 170 pages documenting the stack itself: gates, lint, versioning,