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/modules/insert/pc_crop.rs

@@ -73,6 +73,19 @@ impl PointCloudCropCommand {
         }
     }
 
+    /// The toolbar's crops: the cloud already chosen, the shape too
+    /// ("P" polygon, "C" circle, "" rectangle).
+    pub fn for_cloud(handle: Handle, cloud: ExtendedEntity, option: &str) -> Self {
+        let mut command = Self::new();
+        command.handle = handle;
+        command.cloud = Some(cloud);
+        command.step = Step::First;
+        if !option.is_empty() {
+            command.option(option);
+        }
+        command
+    }
+
     fn data(&self) -> Option<&PointCloudExData> {
         match &self.cloud.as_ref()?.data {
             ExtendedEntityData::PointCloudEx(data) => Some(data),