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/commands/blocks.rs

@@ -715,6 +715,18 @@ impl OpenCADStudio {
                 self.command_line.push_info(&command.prompt());
                 self.tabs[i].active_cmd = Some(Box::new(command));
             }
+            "IMAGECLIP" => {
+                use crate::command::CadCommand;
+                let command = crate::modules::insert::pdf_clip::PdfClipCommand::image();
+                self.command_line.push_info(&command.prompt());
+                self.tabs[i].active_cmd = Some(Box::new(command));
+            }
+            "VPCLIP" => {
+                use crate::command::CadCommand;
+                let command = crate::modules::layout::mview::MviewCommand::vpclip_select();
+                self.command_line.push_info(&command.prompt());
+                self.tabs[i].active_cmd = Some(Box::new(command));
+            }
             "CLIP" => {
                 use crate::command::CadCommand;
                 let command = crate::modules::insert::xclip::ClipCommand::new();