v1.1.0 — Windows installer (Setup.exe)

Adds a native Windows installer, built the same way as macOS: a PyInstaller
onedir app wrapped by Inno Setup into Setup.exe, with Chromium fetched on first
run. Built on a windows-latest CI runner and attached to each release.

Added

• Windows Setup.exe. Download it from the release and run it (unsigned, so
  SmartScreen → More info → Run anyway); BookVault installs to Program Files
  with a Start-menu shortcut. Requires the WebView2 runtime (present on Windows
  11 and up-to-date Windows 10). App data lives in %LOCALAPPDATA%\BookVault;
  Chromium caches in %LOCALAPPDATA%\ms-playwright (shared, survives reinstall).
• CI (.github/workflows/desktop-windows.yml) builds Setup.exe on
  windows-latest on every tag and attaches it to the GitHub Release, and runs
  as a build check on PRs touching the Windows packaging.