feat: PowerShell 7 preflight and launcher - preflight.ps1, wikitool.ps1, doctor policy and Mark of the Web checks, pwsh CI job (#151, B)

Files changed:
- .gitea/workflows/ci.yml
- CHANGES.md
- INSTALL.md
- README.md
- VERSION
- docs/why-gates-are-code.md
- instructions/bootstrap.md
- instructions/bug-report.md
- instructions/preflight.md
- instructions/setup-instance.md
- instructions/upgrade-instance.md
- tools/CONTRACT.md
- tools/README.md
- tools/bugreport.py
- tools/chemenu/cli.py
- tools/chemenu/commands/dist_cmd.py
- tools/chemenu/commands/doctor.py
- tools/chemenu/prerequisites.py
- tools/chemenu/tests/conftest.py
- tools/chemenu/tests/test_bugreport.py
- tools/chemenu/tests/test_doctor.py
- tools/chemenu/tests/test_preflight.py
- tools/chemenu/tests/test_preflight_pwsh.py
- tools/chemenu/toolpaths.py
- tools/preflight.ps1
- tools/wikitool
- tools/wikitool.ps1

instructions/bug-report.md

@@ -176,6 +176,9 @@ Facts only: no page content, no guessed cause, no advice.
   `tree-paths.txt`, which lists every path under `kb/` and `raw/`.
 - **The collector exits 1?** It could not write the bundle (a missing input file, a full disk). Read
   the message, fix the cause, retry once, then report the exact error.
+- **The preflight itself stops, so no Python or venv exists to run the collector?** Its output is
+  the report: take it verbatim from `tools/preflight.sh` or `tools/preflight.ps1`, with the exact
+  command, and add `.wikitool-tools.json` if it was written. Do not install anything to get a bundle.
 - **A `wikitool` output in the bundle looks wrong or refuses to run?** Do not re-run it to see more.
   The bundle records what happened; that is the report.