Add glass_panel widget example; restore rustfmt guard

- New GlassPanel widget (widgets/src/glass_panel.rs) + lib export
- gauss_view: honor surface_alpha for translucent glass surfaces
- examples/glass: standalone demo (wired into Cargo workspace + makepad.splash)
- rustfmt.toml: re-enable disable_all_formatting to stop rustfmt from
  reformatting the whole tree on save

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>