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/scene/render.rs

@@ -636,6 +636,7 @@ impl Scene {
         uniforms.view_proj = crop_view_proj(uniforms.view_proj, uo, vo, us, vs);
         uniforms.viewport_size = [visible_w, visible_h];
         uniforms.flat_shade = if flags.flat_shade { 1.0 } else { 0.0 };
+        uniforms.transparency_enable = if self.transparency_display { 1.0 } else { 0.0 };
 
         // `screen_rect` carries the *visible* sub-rectangle in normalized
         // canvas coords — that's what `Pipeline::prepare` uses to size