feat(statusbar): transparency-display toggle (TPY pill)

Add a transparency_enable uniform read by the wire shader: when the new
TPY pill is off, every line is forced opaque; when on, baked entity
transparency shows through. Toggling is a uniform write, no retessellate
(same mechanism as the lineweight-display toggle). Pill is toggleable
from the status-bar customization menu.

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

src/app/view.rs

@@ -1162,6 +1162,7 @@ impl OpenCADStudio {
                         tab.scene.document.header.insertion_units,
                         self.units_popup_open,
                         tab.scene.is_isolation_active(),
+                        tab.scene.transparency_display,
                         &self.statusbar_config,
                     )
                 })