Manually install 7zip on ARM64 to bypass Scoop extraction issues

On ARM64, directly install 7zip using its silent installer and configure
Scoop to use that external installation. This avoids the 7zr.exe access
denied error in Scoop's extraction process.

🤖 Generated with [Claude Code](https://claude.ai/code)

Co-Authored-By: Claude <[email protected]>

Author: WebKit ARM64 Builder

.github/workflows/build.yml

@@ -294,14 +294,24 @@ jobs:
             echo "$env:USERPROFILE\scoop\shims" | Out-File -FilePath $env:GITHUB_PATH -Encoding utf8 -Append
           }
           
-          # Configure Scoop to use external 7zip for ARM64 to avoid extraction issues
+          # On ARM64, manually install 7zip to avoid Scoop's extraction issues
           if ($isARM64) {
+            $7zipUrl = "https://www.7-zip.org/a/7z2501-arm64.exe"
+            $7zipExe = "$env:TEMP\7z-installer.exe"
+            Invoke-WebRequest -Uri $7zipUrl -OutFile $7zipExe
+            
+            # Extract manually
+            Start-Process -FilePath $7zipExe -ArgumentList "/S", "/D=C:\Program Files\7-Zip" -Wait
+            echo "C:\Program Files\7-Zip" | Out-File -FilePath $env:GITHUB_PATH -Encoding utf8 -Append
+            
+            # Tell Scoop to use the external 7zip we just installed
             scoop config use_external_7zip true
+            scoop config 7zip_path "C:\Program Files\7-Zip\7z.exe"
+          } else {
+            # x64 can use normal Scoop 7zip installation
+            scoop install 7zip
           }
           
-          # Install 7zip
-          scoop install 7zip
-          
           # Install aria2 for parallel downloads
           scoop install aria2