Packaging: Windows MSI gets a setup wizard with version and launch box

Double-clicking the MSI used to flash a progress bar and close, so users couldn't tell it had
installed. It now opens a wizard: Welcome, install folder (remembered across upgrades), Ready,
progress, and a Finish page that says where to find the app with a ticked "Launch VectorCraft"
box. Every page names the full version, pre-release tag included. The wizard art is drawn from
the app icon at package time; msiexec /qn still installs silently.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

docs/releasing.md

@@ -99,6 +99,13 @@ to the target triple, so host build scripts aren't affected.
 - `vectorcraft.wxs` (WiX) is a per-machine install into Program Files with a Start Menu shortcut
   and an App Paths entry (Win+R `vectorcraft`). Same-version upgrades are allowed, so release
   candidates replace each other.
+- Double-clicking the MSI opens a setup wizard (WixUI_InstallDir without the licence page):
+  Welcome, install folder (remembered for upgrades in `HKLM\Software\VectorCraft\InstallDir`),
+  Ready, a progress page, and a Finish page that says where to find the app, with a ticked "Launch
+  VectorCraft" box. The pages name the full version (`vectorcraft.en-us.wxl`). `package.ps1` draws
+  the wizard's banner and side bitmaps from the app icon, so no WiX stock art ships. `msiexec /qn`
+  still installs silently. Building needs the WiX UI and Util extensions:
+  `wix extension add -g WixToolset.UI.wixext/5.0.2 WixToolset.Util.wixext/5.0.2`.
 - The ARM64 build is cross-compiled on the x64 runner. `.github/workflows/windows-arm64.yml`
   installs that MSI on a Windows 11 ARM64 runner, checks that both installed programs are ARM64,
   runs `vectorcraft-cli --version` natively and uninstalls.