M2: shell and draft (exact convex polyhedra from planes)

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

crates/ui-egui/src/timeline.rs

@@ -24,6 +24,8 @@ fn icon_of(k: &FeatureKind) -> &'static str {
         FeatureKind::Mirror { .. } => "mirror",
         FeatureKind::ConstructionPlane { .. } => "plane",
         FeatureKind::Hole { .. } => "hole",
+        FeatureKind::Shell { .. } => "shell",
+        FeatureKind::Draft { .. } => "draft",
         FeatureKind::Split { .. } => "split",
         FeatureKind::Move { .. } => "move",
     }