perf(render): instance block geometry

Share source buffers across block placements and render nested content with GPU instance transforms.\n\nChunk silhouettes and compact mesh material data so large drawings stay under device buffer limits and remain responsive.

src/scene/model/wire_model.rs

@@ -156,6 +156,8 @@ pub struct WireModel {
     /// `true` only for a planar SOLID entity's interior. Wireframe 3D omits
     /// this fill while preserving its perimeter and every other 2-D overlay.
     pub fill_is_2d_solid: bool,
+    /// Shared block-render source and this placement's translation.
+    pub render_instance: Option<super::instance_model::RenderInstance>,
 }
 
 impl WireModel {
@@ -208,6 +210,7 @@ impl WireModel {
             depth_override: None,
             fill_is_3d: false,
             fill_is_2d_solid: false,
+            render_instance: None,
             pick_tris: Vec::new(),
             pick_tris_low: Vec::new(),
             text_verts: Vec::new(),
@@ -467,6 +470,7 @@ impl Default for WireModel {
             depth_override: None,
             fill_is_3d: false,
             fill_is_2d_solid: false,
+            render_instance: None,
             pick_tris: Vec::new(),
             pick_tris_low: Vec::new(),
         }