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

tools/CONTRACT.md

@@ -61,6 +61,8 @@ from the repo root:
 tools/preflight.sh
 ```
 
+From PowerShell 7 on Windows, the twin: `pwsh -NoProfile -ExecutionPolicy Bypass -File tools/preflight.ps1`.
+
 Until it has passed, every `tools/wikitool` call exits 42 and names it.
 
 ## Usage
@@ -3221,8 +3223,9 @@ Check that this instance is correctly configured.
 **NOTES**
 
 - Checks dependencies (Python, ripgrep), author resolution, stack version, git identity/branch/remote, published skills, the kb/raw/reports/work/instructions structure, and generated files.
-- Tool paths (`tool-paths`): `.wikitool-tools.json` written by a preflight that finished, every tool `tools/prerequisites.txt` names for this platform recorded, and every recorded path still there - a `FAIL` otherwise, fixed by running `tools/preflight.sh` again.
+- Tool paths (`tool-paths`): `.wikitool-tools.json` written by a preflight that finished, every tool `tools/prerequisites.txt` names for this platform recorded, and every recorded path still there - a `FAIL` otherwise, fixed by running `tools/preflight.sh` again (PowerShell 7: `tools/preflight.ps1`).
 - Install folder (`install-dir`): on Windows with long paths off, a `FAIL` when the folder holding `tools/` is longer than `tools/prerequisites.txt` allows (95 characters) - the limit the preflight enforces before it sets anything up.
+- PowerShell (`execution-policy`, `script-marks`; Windows only, `OK` elsewhere): a `FAIL` when the effective execution policy is `Restricted` or `AllSigned` - the line then says whether a group policy sets it, which only whoever administers the computer can change - and a `FAIL` when a script under `tools/` carries a Mark of the Web from the internet zone, which a browser download unpacked in Explorer leaves behind and `Invoke-WebRequest` plus `tar` do not. `tools/preflight.ps1` checks the same two things before it stops.
 - Personalization: `USER.md`/`SOUL.md` present **and** filled - a file still carrying the template's sentinel is a `FAIL`.
 - KB conventions: `kb/CONVENTIONS.md` present, unsentinelled, and naming all three tool-owned section headings - a `FAIL` on any of the three.
 - Environment note: `ENVIRONMENT.md` is optional, so absent is `OK`; a still-templated one is a `WARN`.