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 <[email protected]>

src/scene/mod.rs

@@ -553,6 +553,9 @@ pub struct Scene {
     /// `tessellate_block`'s visibility test skips these, so they neither
     /// render nor hit-test until isolation ends.
     pub hidden: HashSet<Handle>,
+    /// Whether entity transparency is honoured on screen. When false the
+    /// wire shader forces every line opaque (a uniform toggle, no retessellate).
+    pub transparency_display: bool,
     /// In-progress preview wires while a command is active (rubber-band + object ghosts).
     pub preview_wires: Vec<WireModel>,
     /// Committed-segment wire drawn during multi-point commands (normal colour).
@@ -698,6 +701,7 @@ impl Scene {
             document: CadDocument::new(),
             selected: HashSet::new(),
             hidden: HashSet::new(),
+            transparency_display: true,
             preview_wires: vec![],
             interim_wire: None,
             camera_generation: 0,

src/scene/pipeline/uniforms.rs

@@ -19,9 +19,13 @@ pub struct Uniforms {
     /// triangle gets a uniform shade (FlatShaded mode); 0.0 → keeps the
     /// per-vertex normal interpolation (GouraudShaded-style).
     pub flat_shade: f32,
+    /// Transparency-display toggle (1.0 = honour entity transparency,
+    /// 0.0 = force opaque). Read by the wire shader so the toggle does not
+    /// require a retessellate.
+    pub transparency_enable: f32,
     /// Pads the struct to 112 B (next multiple of 16) so wgpu's uniform
     /// alignment rules are satisfied.
-    pub _pad: [f32; 3],
+    pub _pad: [f32; 2],
 }
 
 impl Uniforms {
@@ -39,7 +43,8 @@ impl Uniforms {
             world_per_pixel,
             lwdisplay_enable: if lwdisplay_enable { 1.0 } else { 0.0 },
             flat_shade: 0.0,
-            _pad: [0.0; 3],
+            transparency_enable: 1.0,
+            _pad: [0.0; 2],
         }
     }
 }

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