model: resolve_set_partial, and the rotating-node rule as Model::rotational_nodes

resolve_set_partial resolves the members of a set that are on the mesh, for
display: a set with a missing member still shows what it has, where
resolve_set refuses it. rotational_nodes is the check's rule for which nodes
have rotations (shell and beam nodes, not those of 2D sections), so the
viewport's symbols and the check agree.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01NmAttHhUZTokgPeEJia8sm

crates/model/tests/definition.rs

@@ -516,3 +516,13 @@ fn two_dimensional_models_resolve_edges_and_check_their_rules() {
         assert!(m.add_load("hostile", bad.clone()).is_err(), "{bad:?}");
     }
 }
+
+#[test]
+fn display_resolves_what_is_on_the_mesh() {
+    let mut m = defined();
+    // A set with a node the mesh does not have: the check refuses it, the display shows the rest.
+    m.add_set("half", Set { nodes: vec![1, 999], ..Set::default() }).unwrap();
+    assert!(m.resolve_set("half").is_err());
+    assert_eq!(m.resolve_set_partial("half").map(|r| r.nodes), Some(vec![1]));
+    assert_eq!(m.resolve_set_partial("nope"), None);
+}