feat: put ncp on PATH on both platforms; rename WSL reqs to Windows

Ports the ncp PATH work from upstream. Registering ncp as a shell-profile
function failed three ways on Windows: the default Restricted execution policy
blocks the profile itself, profiles don't exist outside PowerShell (cmd, Win+R,
Task Scheduler), and the self-elevating installer writes the admin's profile.

Windows now ships management/ncp.cmd and the installer appends management\ to
the Machine PATH via [Environment]::SetEnvironmentVariable -- never setx, which
truncates PATH at 1024 chars. A .cmd is exempt from the execution policy.

Linux symlinks /usr/local/bin/ncp -> management/nexus-cli.sh, falling back to
the old .bashrc function when sudo is unavailable.

Also renames requirements-wsl.txt to requirements-windows.txt and purges stale
WSL references, including vite.config.js's dev-server comment and
controlpanel.py's "Check WSLg." error string.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

management/ncp.cmd

@@ -0,0 +1,16 @@
+@echo off
+REM ncp - PATH entry point on Windows. A .cmd, not a .ps1, on purpose: PowerShell's
+REM execution policy governs .ps1 only, so this keeps working under the default
+REM Restricted policy and from cmd, Win+R, Task Scheduler and .lnk targets - none
+REM of which load a PowerShell profile. install-windows.ps1 puts this directory on
+REM the machine PATH. ncp.ps1 stays for pwsh-on-Linux, where there is no PATH shim.
+REM
+REM ASCII only, same rule as the .ps1 files - a test in tests/test_smoke.py enforces it.
+setlocal
+set "ROOT=%~dp0.."
+REM System Python fallback so backup/restore work before the venv exists; those
+REM delegate to the stdlib-only bin/sync.py. Mirrors the same fallback in ncp.ps1.
+set "PY=%ROOT%\Promethean\Scripts\python.exe"
+if not exist "%PY%" set "PY=python"
+"%PY%" "%ROOT%\management\ncp.py" %*
+exit /b %ERRORLEVEL%