feat(installer): add finish screen with launch-app checkbox to Windows MSI

Adds WixUI_Minimal UI to the WiX installer so users see a proper
Welcome → Progress → Finish wizard. The finish screen includes a
pre-ticked "Launch Open CAD Studio" checkbox; clicking Finish with
it checked starts the application immediately after the installer closes.

Also updates the light.exe invocation in release.yml to include
-ext WixUIExtension, which is required to link the WixUI dialogs.

https://claude.ai/code/session_01DFVSKgViFaxEjZD2KsTdtt

.github/workflows/release.yml

@@ -138,7 +138,7 @@ jobs:
             $wxsPath `
             -out $wixObj
           if ($LASTEXITCODE -ne 0) { throw "candle failed" }
-          & $light $wixObj -out $msiPath
+          & $light $wixObj -ext WixUIExtension -out $msiPath
           if ($LASTEXITCODE -ne 0) { throw "light failed" }
 
       - name: Sign MSI installer (Azure Trusted Signing)

packaging/windows/main.wxs

@@ -6,7 +6,7 @@
     candle.exe -arch x64 -dVersion=<x.y.z> -dSource=target\release\OpenCADStudio.exe \
                -dIcon=packaging\windows\AppIcon.ico packaging\windows\main.wxs \
                -out packaging\windows\main.wixobj
-    light.exe  packaging\windows\main.wixobj -out OpenCADStudio.msi
+    light.exe  packaging\windows\main.wixobj -ext WixUIExtension -out OpenCADStudio.msi
 
   Provides:
     * Per-machine install under Program Files\Open CAD Studio.
@@ -122,5 +122,35 @@
       <ComponentRef Id='ProgramMenuDirComp' />
     </Feature>
 
+    <!--
+      Finish-screen "Launch Open CAD Studio" checkbox.
+      WIXUI_EXITDIALOGOPTIONALCHECKBOX=1 pre-ticks the checkbox; the Publish
+      below fires the launch action when the user clicks Finish with it checked.
+      WixUI_Minimal shows a minimal wizard (Welcome → Progress → Finish).
+    -->
+    <Property Id='WIXUI_EXITDIALOGOPTIONALCHECKBOXTEXT' Value='Launch Open CAD Studio' />
+    <Property Id='WIXUI_EXITDIALOGOPTIONALCHECKBOX' Value='1' />
+
+    <!--
+      Start the installed exe after the wizard closes.
+      asyncNoWait lets the installer exit cleanly while the app starts.
+    -->
+    <CustomAction
+      Id='LaunchApplication'
+      FileKey='OpenCADStudioEXE'
+      ExeCommand=''
+      Execute='immediate'
+      Return='asyncNoWait'
+      Impersonate='yes' />
+
+    <UI>
+      <UIRef Id='WixUI_Minimal' />
+      <Publish
+        Dialog='ExitDialog'
+        Control='Finish'
+        Event='DoAction'
+        Value='LaunchApplication'>WIXUI_EXITDIALOGOPTIONALCHECKBOX = 1 AND NOT Installed</Publish>
+    </UI>
+
   </Product>
 </Wix>