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/view/mod.rs

@@ -1604,6 +1604,11 @@ bg={bg_ms:.1}ms n={view_count}"
                 None
             } else if self.ribbon.xref_context() {
                 crate::ui::side_toolbar::view(&crate::ui::ribbon::xref_tools())
+            } else if let Some(shown) = self.ribbon.point_cloud_context() {
+                crate::ui::side_toolbar::view_with_active(
+                    &crate::ui::ribbon::point_cloud_tools(),
+                    &move |id| id == "_PCCROPSHOW" && shown,
+                )
             } else if let Some(ctx) = self.ribbon.underlay_context() {
                 let ctx = ctx.clone();
                 crate::ui::side_toolbar::view_with_active(