fix(widget): recover delayed X11 frame-sync stalls

[attson]

Summary

• disable GTK X11 frame sync before the widget first paints, with a Ready fallback
• detect an extended XSync counter stuck odd and recover via a geometry-preserving hide/show
• preserve above/attention state and package the new libXext runtime dependency

Verification

• go vet -tags webkit2_41 ./...
• cd desktop/frontend && npm run build
• go test -tags webkit2_41 -timeout 60s ./desktop/ -count=1
• 64 widget frontend tests
• production wails build -tags webkit2_41 -skipbindings
• fault injection: odd counter recovered, animation resumed, geometry and ABOVE preserved, no final DEMANDS_ATTENTION
• Deb dry run: Depends: libgtk-3-0, libwebkit2gtk-4.1-0, libxext6