[codex] Add grouped WPF update list

[Darkaxt]

Summary

• Replace the WPF active update table with grouped category cards for Windows Update, Installed Updates, and Hidden Updates.
• Keep Update History on the dense table layout.
• Add tri-state group selection, expand/collapse behavior, and keep Select All scoped to visible active-list rows.
• Refresh README/user-guide screenshots and docs for the grouped category behavior.

Validation

• git diff --check
• MSBuild.exe wumgr.sln /p:Configuration=Release /p:Platform="Any CPU" /m /v:minimal
• wumgr.Tests\bin\Release\wumgr.Tests.exe
• Visual smoke check of refreshed light/dark WPF screenshots.