feat: preflight - prerequisites checked and tool paths recorded before wikitool runs; launcher refuses without it (#151, POSIX half)

Files changed:
- .claude/settings.json
- .gitea/workflows/ci.yml
- .gitea/workflows/nightly.yml
- .gitea/workflows/release.yml
- .gitea/workflows/tracker-live.yml
- .github/hooks/wiki-trace.json
- .gitignore
- .vibe/hooks.toml
- AGENTS.md
- CHANGES.md
- EVALS.md
- INSTALL.md
- README.md
- VERSION
- instructions/bootstrap.md
- instructions/preflight.md
- instructions/setup-instance.md
- instructions/upgrade-instance.md
- tools/CONTRACT.md
- tools/README.md
- tools/chemenu/cli.py
- tools/chemenu/commands/dist_cmd.py
- tools/chemenu/commands/docs_verify.py
- tools/chemenu/commands/doctor.py
- tools/chemenu/commands/git_publish.py
- tools/chemenu/commands/migrate_cmd.py
- tools/chemenu/config.py
- tools/chemenu/corpus_cache.py
- tools/chemenu/prerequisites.py
- tools/chemenu/search/ripgrep.py
- tools/chemenu/tests/conftest.py
- tools/chemenu/tests/test_dist_upgrade.py
- tools/chemenu/tests/test_doctor.py
- tools/chemenu/tests/test_preflight.py
- tools/chemenu/toolpaths.py
- tools/preflight.sh
- tools/prerequisites.txt
- tools/run_wikitool.py
- tools/trace-hook
- tools/wikitool

tools/run_wikitool.py

@@ -0,0 +1,14 @@
+"""What tools/wikitool and tools/wikitool.ps1 run with the venv's Python.
+
+Running a file puts its own directory at the front of `sys.path`, so `chemenu`
+imports from here without `PYTHONPATH` - whose separator is `:` on POSIX and `;`
+on Windows, one more thing for two launchers to get right.
+
+The name deliberately does not start with `wikitool.`: the Windows Python
+installer can add `.PY` to `PATHEXT`, and a `tools/wikitool.py` could then be
+what PowerShell runs for `tools/wikitool`.
+"""
+from chemenu.cli import main
+
+if __name__ == "__main__":
+    main()