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/preflight.md

@@ -9,15 +9,28 @@ description: Run the preflight before any wikitool command in a new, cloned, mov
 exit 42 and names this procedure instead - so there is no skipping it, only running it early
 or being sent back to it.
 
-The preflight is a shell script, not a `wikitool` command, because it has to work before
-Python is known to exist. It does three things, all inside the install folder:
+The preflight is a script, not a `wikitool` command, because it has to work before Python is
+known to exist: `tools/preflight.sh` for POSIX shells, `tools/preflight.ps1` for PowerShell 7 on
+Windows. The two answer the same questions from the same list and write the same
+`.wikitool-tools.json`. It does three things, all inside the install folder:
 
 - checks the tools listed in `tools/prerequisites.txt` - Python 3.11 or newer, git, ripgrep
-  (`rg`) - and, on Windows, that the install folder is short enough for Windows' path limit;
+  (`rg`) - and, on Windows, that the install folder is short enough for Windows' path limit and
+  (PowerShell only) that the execution policy and the files' Mark of the Web let
+  `tools/wikitool.ps1` start;
 - records the absolute path of each tool in `.wikitool-tools.json`, which `wikitool` then starts
   them from instead of trusting whatever `PATH` a session inherited;
 - creates `tools/.venv` from the recorded Python and installs `tools/requirements.txt` into it.
 
+<!-- wikitool:toc -->
+## Contents
+
+- [When to run](#when-to-run)
+- [Steps](#steps)
+- [Decision points](#decision-points)
+- [Scope](#scope)
+<!-- /wikitool:toc -->
+
 ## When to run
 
 - First step of every installation procedure: [setup-instance.md](setup-instance.md) and
@@ -25,20 +38,29 @@ Python is known to exist. It does three things, all inside the install folder:
 - After every stack update ([upgrade-instance.md](upgrade-instance.md)) - a release can change
   what the machine needs, or the requirements the venv holds.
 - Whenever `tools/wikitool` exits 42 and names the preflight, and whenever `tools/wikitool doctor`
-  reports `tool-paths` or `install-dir` as `FAIL`.
+  reports `tool-paths`, `install-dir`, `execution-policy` or `script-marks` as `FAIL`.
 
 It is safe to run at any time: a second run on a ready checkout changes nothing and exits 0.
 
 ## Steps
 
-1. **Run it** from the root of the checkout:
+1. **Run it** from the root of the checkout, with the script for the shell the session runs in:
 
    ```bash
    tools/preflight.sh
    ```
 
    This covers Linux, macOS and Git Bash on Windows, which is where Claude Code runs its
-   commands there.
+   commands there. From PowerShell 7 on Windows (GitHub Copilot CLI, for one) use the twin, and
+   always with exactly this prefix:
+
+   ```powershell
+   pwsh -NoProfile -ExecutionPolicy Bypass -File tools/preflight.ps1
+   ```
+
+   The bypass holds for that one process only and changes no setting; it is what lets the script
+   run at all when the checkout carries a Mark of the Web, so that it can report that itself.
+   Windows PowerShell 5.1 is not supported.
 
 2. **Read the exit code.**
 
@@ -67,6 +89,10 @@ It is safe to run at any time: a second run on a ready checkout changes nothing
    tools/preflight.sh --set rg=/opt/ripgrep/rg
    ```
 
+   ```powershell
+   pwsh -NoProfile -ExecutionPolicy Bypass -File tools/preflight.ps1 --set rg=C:\Tools\rg\rg.exe
+   ```
+
    `--set <tool>=<path>` may be given several times. A path that does not work is refused with
    exit 42 and nothing is written; a working one is recorded and kept on later runs, even though
    the tool is still not on `PATH`.
@@ -77,6 +103,15 @@ It is safe to run at any time: a second run on a ready checkout changes nothing
   install folder may be at most 95 characters, because every file of the wiki below it has to
   stay within 259. Moving the wiki to a shorter folder is the user's step; do not try to shorten
   paths inside the wiki instead.
+- **The output names the PowerShell execution policy** (`Restricted` or `AllSigned`). The fix is a
+  line the user runs in a PowerShell 7 window; it changes a setting of their account, so it is
+  theirs to run. When a *group policy* sets it, nothing on this computer can override it: the
+  output says to ask whoever administers the machine - or to use `tools/wikitool` from Git Bash
+  instead. Do not suggest a workaround that evades the policy.
+- **The output names scripts with a Mark of the Web.** The checkout was downloaded with a browser
+  and unpacked in Explorer, so Windows marks every file as coming from the internet. The command
+  in the output (`Unblock-File` over the folder) is the user's to run; a download by
+  `Invoke-WebRequest`, `git clone` or `tar` carries no mark.
 - **The venv or its libraries could not be installed.** The output carries the last lines of
   what Python or pip said. A network, proxy or security-product cause is for the user - or
   whoever administers their machine - to resolve; do not retry with other flags.