geometry: partition cuts and the projection mesher report progress and stop when cancelled

Co-Authored-By: Claude Opus 5.5 <[email protected]>
Claude-Session: https://claude.ai/code/session_01UhhZMBTviDQxZvwnyP89fo

crates/engine/src/lib.rs

@@ -87,6 +87,7 @@ impl EngineError {
         matches!(
             self,
             EngineError::Model(Cancelled)
+                | EngineError::Geometry(fieldcraft_geometry::Error::Model(Cancelled))
                 | EngineError::Mesh(fieldcraft_mesh::Error::Model(Cancelled))
                 | EngineError::Solver(fieldcraft_solver::Error::Model(Cancelled))
                 | EngineError::Explicit(fieldcraft_explicit::Error::Model(Cancelled))