docs(windows): add native Windows guide + install one-liner on landing page (#22089)

New page: website/docs/user-guide/windows-native.md — comprehensive
Windows-native deep dive covering:

- Quick install (irm | iex) and parameterized form
- What the installer does end-to-end (uv, Python 3.11, Node 22,
  PortableGit, messaging SDK bootstrap)
- Feature matrix: native Windows vs WSL2 (dashboard /chat is WSL-only)
- How Hermes runs shell commands on Windows (Git Bash resolution,
  HERMES_GIT_BASH_PATH override, MinGit layout pitfall)
- UTF-8 console shim (configure_windows_stdio, opt-out via
  HERMES_DISABLE_WINDOWS_UTF8)
- Editor handling (notepad default, VSCode/Notepad++/nvim overrides,
  why Ctrl-X Ctrl-E used to silently do nothing)
- Ctrl+Enter for newline in the CLI
- Gateway as a Scheduled Task (schtasks + Startup-folder fallback,
  pythonw.exe detached spawn, why not a Windows Service)
- Data layout (%LOCALAPPDATA%\hermes vs %USERPROFILE%\.hermes split)
- PATH after install, environment variables, uninstall
- Process management internals (bpo-14484 os.kill(pid, 0) footgun,
  _pid_exists primitive, check-windows-footguns.py CI gate)
- 10+ concrete pitfalls with fixes

Also:
- docs/index.md: add inline 'Install' section with both Linux/macOS
  curl and Windows irm|iex one-liners right under the hero CTAs.
  Updates the quick-links row to include 'native Windows'.
- sidebars.ts: add Windows (Native) entry above Windows (WSL2).
- windows-wsl-quickstart.md: point native-install cross-link at the
  new dedicated page (was going to installation.md#windows-native).
- reference/environment-variables.md: document HERMES_GIT_BASH_PATH
  and HERMES_DISABLE_WINDOWS_UTF8 (previously undocumented).

website/docs/user-guide/windows-wsl-quickstart.md

@@ -7,7 +7,7 @@ sidebar_position: 2
 
 # Windows (WSL2) Guide
 
-Hermes Agent now supports **both** native Windows and WSL2.  This page covers the WSL2 path; for the native PowerShell install see [Installation](../getting-started/installation.md#windows-native-powershell).
+Hermes Agent now supports **both** native Windows and WSL2.  This page covers the WSL2 path; for the native PowerShell install see the dedicated **[Windows (Native) Guide](./windows-native.md)**.
 
 **When to pick WSL2 over native:**
 - You want to use the dashboard's embedded terminal (`/chat` tab) — that pane requires a POSIX PTY and is WSL2-only.