converters: Testkorpus und Harness ziehen nach torben/chemenu-testfiles, Workflow Converters mit Pfad-Trigger, Release-Gate (#232); 10.1.0-beta.2

Files changed:
- .gitattributes
- .gitea/workflows/converters.yml
- .gitea/workflows/release.yml
- .gitignore
- CHANGES.md
- VERSION
- docs/dev/development.md
- instructions/dev/dev-setup.md
- instructions/dev/publish-and-ci.md
- instructions/dev/testing-conventions.md
- testfiles/README.md
- testfiles/mail/github-outlook.msg
- testfiles/mail/github-roundcube.eml
- testfiles/mail/gog-outlook.msg
- testfiles/mail/gog-roundcube.eml
- testfiles/mail/gog-roundcube.eml.expect
- testfiles/mail/tldr-outlook.msg
- testfiles/mail/tldr-roundcube.eml
- testfiles/office/excel-artificial.xlsx
- testfiles/office/excel-business.xlsx
- testfiles/office/excel-business.xlsx.expect
- testfiles/office/excel-science.xlsx
- testfiles/office/pptx-baseline.pptx
- testfiles/office/pptx-master.pptx
- testfiles/office/pptx-objects.pptx
- testfiles/office/word-complex.docx
- testfiles/office/word-simple.docx
- testfiles/pdf/einstein-dissertation.pdf
- testfiles/pdf/ifg.pdf
- testfiles/pdf/nist-ai-rmf.pdf
- testfiles/pdf/nist-ssdf-genai.pdf
- testfiles/zip/archive.zip
- tools/chemenu/tests/test_raw_derive_testfiles.py

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

instructions/dev/testing-conventions.md

@@ -187,7 +187,15 @@ Whenever you add or change a test under `tools/chemenu/tests/`.
 
 ## Scope
 
-Applies to `tools/chemenu/tests/` only. It says nothing about what to test - the test/review
+Applies to `tools/chemenu/tests/` only. Tests against **real documents** are not among them:
+they live in the private repository `chemenu-testfiles` (`harness/`, with the corpus beside it),
+cloned into the gitignored `testfiles/` ([dev-setup.md](dev-setup.md) step 6) and run with this
+checkout's `tools/.venv` by the `converters` workflow. A new file for the corpus is a case for
+that harness, not a fixture here; the synthetic filter tests (`test_raw_derive.py`,
+`test_raw_derive_binary.py`) stay and are what the suite relies on. The harness borrows this
+suite's `conftest.py`, so a change to a fixture there reaches it too.
+
+This file says nothing about what to test - the test/review
 expectations for a stack change are the local checks in [publish-and-ci.md](publish-and-ci.md)
 (`docs verify`, `instructions verify`, pytest), run from `stack-build`. CI runs the suite once,
 unhardened, because the fixture makes a second hardened run redundant; see the note on the Tests