G1: Grid tool dialogs add reference point locator (#1377)

Rectangular and Polar Grid click dialogs show the nine-point locator and resize width/height about it using the same artboard_rect logic as Artboard Options.

Co-authored-by: Cursor <cursoragent@cursor.com>

crates/ui-egui/src/dialogs/tests_rectangular_grid.rs

@@ -159,6 +159,20 @@ fn key_frame(app: &mut VectorcraftApp, key: egui::Key) {
     out.textures_delta.clear();
 }
 
+/// #1377: OK uses the bounding box after a reference-point resize (`artboard_rect` keeps the
+/// center pinned when width doubles).
+#[test]
+fn rectangular_grid_reference_point_pins_center_when_width_changes() {
+    let mut app = app();
+    click(&mut app, Point::new(100.0, 100.0));
+    assert_eq!(field(&app, "reference"), json!(0));
+    for (key, value) in [("reference", json!(4)), ("x", json!(50.0)), ("y", json!(50.0)), ("width", json!(200)), ("height", json!(100))] {
+        set(&mut app, key, value);
+    }
+    let id = confirm(&mut app);
+    assert_grid(&app, id, Rect::new(50.0, 50.0, 250.0, 150.0), 5, 5);
+}
+
 #[test]
 fn rectangular_grid_canvas_click_opens_registered_dialog_with_saved_counts_and_point_defaults() {
     let mut app = app();