fix(build): clean compile before publish (CI shipped stale Core.dll)

The deployed toolbox Core.dll was timestamped BEFORE its own build ran -- the CI runner's
incremental build reused a cached SilverOS.Welcome.Core.dll, so source fixes (e.g. the winget
bootstrap brace fix) never reached the published exe. Wipe all bin/obj under welcome/ and pass
--no-incremental so every build is a clean compile.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

windows/installer/build.ps1

@@ -160,7 +160,12 @@ function Invoke-PublishWelcome {
     Write-Stage 'Stage 3b: publish SilverOS Welcome app (win-x64 self-contained)'
     $proj = Join-Path $WindowsDir 'welcome\src\SilverOS.Welcome.App'
     $out  = Join-Path $WorkDir 'welcome-publish'
-    & dotnet publish $proj -c Release -f net9.0-windows10.0.19041.0 -r win-x64 --self-contained true -o $out
+    # Force a CLEAN compile. The CI runner reuses build artifacts across runs, and dotnet's
+    # incremental build has shipped a STALE SilverOS.Welcome.Core.dll (old code despite fixed
+    # source) -- so wipe every bin/obj under welcome/ and pass --no-incremental.
+    Get-ChildItem (Join-Path $WindowsDir 'welcome') -Recurse -Directory -EA SilentlyContinue |
+        Where-Object { $_.Name -in 'bin', 'obj' } | Remove-Item -Recurse -Force -EA SilentlyContinue
+    & dotnet publish $proj -c Release -f net9.0-windows10.0.19041.0 -r win-x64 --self-contained true --no-incremental -o $out
     if ($LASTEXITCODE -ne 0) { throw 'Welcome app dotnet publish failed' }
     Write-Host "   Published to: $out"
 }