UI: compile fix for the new feature kinds (Hole pattern rest, timeline icon fallback)

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01AS5Tn3xieewUSg3uxrMVdL

crates/ui-egui/src/timeline.rs

@@ -31,6 +31,7 @@ fn icon_of(k: &FeatureKind) -> &'static str {
         FeatureKind::Split { .. } => "split",
         FeatureKind::Move { .. } => "move",
         FeatureKind::Import { .. } | FeatureKind::MeshImport { .. } => "import",
+        _ => "feature",
     }
 }