Add Windows support for the "Open in editor" button

[PythonLuvr]

Same as the Linux issue, but for Windows. Editors and install paths to detect:

• VS Code: code.cmd on PATH, or %LOCALAPPDATA%\Programs\Microsoft VS Code\bin\code.cmd
• Cursor: cursor.cmd on PATH, or %LOCALAPPDATA%\Programs\Cursor\Cursor.exe
• Windsurf: similar pattern under %LOCALAPPDATA%\Programs\
• Zed: zed.exe on PATH if installed

File to extend: app/api/fs/open-editor/route.ts. Note that on Windows you'll likely want to spawn with shell: true so .cmd shims resolve correctly.

Acceptance: on Windows, the editor menu shows whichever of the above are installed; clicking one opens the project path.