Point clouds: attach dialog, crop toolbar, stylize, palette rows

POINTCLOUDATTACH opens the Attach Point Cloud dialog after the file is
chosen; its Attach button lives in the Attach Underlay list instead of a
separate Insert panel. A selected cloud brings the crop tools to the
right-edge toolbar. POINTCLOUDSTYLIZE sets the stylization with the
reference's prompts, the External References palette lists point clouds
(unload, reload, detach, path), and definitions keep the header extents.

Co-Authored-By: Claude Opus 5.5 <[email protected]>

src/app/mod.rs

@@ -497,6 +497,7 @@ pub(super) struct OpenCADStudio {
     block_definition: Option<crate::ui::window::block_definition::BlockDefinitionState>,
     /// PDF dialogs' working copies; `None` while closed.
     pdf_attach: Option<crate::ui::window::pdf_dialogs::PdfAttachState>,
+    point_cloud_attach: Option<crate::ui::window::pdf_dialogs::PointCloudAttachState>,
     underlay_layers: Option<crate::ui::window::pdf_dialogs::UnderlayLayersState>,
     pdf_import_settings: Option<crate::modules::insert::pdf_import::PdfImportSettings>,
     pdf_import_file: Option<crate::ui::window::pdf_dialogs::PdfImportFileState>,
@@ -1901,6 +1902,7 @@ pub enum ModalKind {
     DrawingUnits,
     BlockDefinition,
     PdfAttach,
+    PointCloudAttach,
     UnderlayLayers,
     PdfImportSettings,
     PdfImportFile,
@@ -4031,6 +4033,7 @@ impl OpenCADStudio {
             drawing_units: None,
             block_definition: None,
             pdf_attach: None,
+            point_cloud_attach: None,
             underlay_layers: None,
             pdf_import_settings: None,
             pdf_import_file: None,