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/upgrade-instance.md

@@ -161,6 +161,13 @@ fresh clone ([bootstrap.md](bootstrap.md)), and not for the clone-with-upstream
    tools/wikitool instructions sync
    ```
 
+   From PowerShell 7 on Windows, run the twin instead - same questions, same file:
+
+   ```powershell
+   pwsh -NoProfile -ExecutionPolicy Bypass -File tools/preflight.ps1
+   tools/wikitool instructions sync
+   ```
+
    `instructions sync` is needed because the published skill directories are copies: until it
    runs, the harness is still offering the previous release's skills.