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>

requirements-windows.txt

@@ -0,0 +1,14 @@
+# Windows / CPU-only install — runtime stack, no GPU deps
+
+fastapi
+uvicorn[standard]
+httpx
+requests
+pydantic
+PyYAML
+python-dotenv
+psutil
+
+# Native desktop window for the UI (WebView2 on Windows; pulls pythonnet).
+# Used by bin/nexus_window.py, launched from launch_nexus.ps1.
+pywebview