feat(windows): icon, windowed exe, no-admin installer

- PyInstaller exe built windowed (console=False) with package/testium.ico
  as the embedded icon (BMP entries for shell compatibility).
- Suppress stray subprocess console windows in the frozen Windows build via
  paths.no_window_kwargs() (CREATE_NO_WINDOW); wheel/source unchanged.
  Applied to py_process, lua_process, bins probes, sys_app_path_win.
- New per-user Inno Setup installer (package/innosetup/): no admin,
  version-scoped AppId/dir so versions install side-by-side, one Start
  Menu entry per version, .ico shipped for shortcut/uninstall icons.
- DESIGN.md + release_note.txt updated.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

release_note.txt

@@ -7,6 +7,7 @@ version 0.2.3
   wrapper (run.bat).
 - Resolved python_bin / lua_bin are now published into the global dict,
   so test scripts can read them via $(python_bin) / $(lua_bin).
+- Windows: new per-user installer (no admin).
 
 version 0.2.2
 ==============