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 <noreply@anthropic.com>

src/app/control/actions.rs

@@ -713,6 +713,7 @@ impl OpenCADStudio {
                 use crate::ui::window::pdf_dialogs::PdfDialogMsg;
                 Message::PdfDialog(match self.active_modal {
                     Some(crate::app::ModalKind::PdfAttach) => PdfDialogMsg::AttachOk,
+                    Some(crate::app::ModalKind::PointCloudAttach) => PdfDialogMsg::CloudOk,
                     Some(crate::app::ModalKind::UnderlayLayers) => PdfDialogMsg::LayersOk,
                     Some(crate::app::ModalKind::PdfImportSettings) => PdfDialogMsg::SettingsOk,
                     Some(crate::app::ModalKind::PdfImportFile) => PdfDialogMsg::ImportOk,