CLIP on raster images and viewports, IMAGECLIP, VPCLIP, clip depth rules

- CLIP continues as IMAGECLIP on a raster image and as VPCLIP on a layout
  viewport, with the reference prompts and stored data.
- Image clip boundaries sit on pixel centres, OFF only clears the display
  flag, and an inverted boundary cuts the image.
- VPCLIP polygon (Arc/Length/Close/Undo), clipping object and Delete; the
  viewport shrinks to the boundary's exact extents, view kept.
- XCLIP Clipdepth: Remove clears only the plane asked, a front plane behind
  the back one is rejected with the reference message.
- Attached and imported images carry the reference display flags.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

src/app/command_driver/mod.rs

@@ -471,8 +471,11 @@ impl OpenCADStudio {
             CmdResult::MviewCreateClipped {
                 boundary,
                 boundary_handle,
+                target,
             } => {
-                if let Some(task) = self.handle_mview_create_clipped(boundary, boundary_handle) {
+                if !target.is_null() {
+                    self.handle_vpclip(target, boundary, boundary_handle);
+                } else if let Some(task) = self.handle_mview_create_clipped(boundary, boundary_handle) {
                     return task;
                 }
             }