DWF/DGN underlays: clipping, layers, text, 3D DGN, colours and zoom extents

- PDFOSNAP, DWFOSNAP and DGNOSNAP are separate; UOSNAP sets them all and
  reads 2 while they differ. Enable Snap switches the selected kind's.
- DWFCLIP / DGNCLIP clip their own kind with the kind's prompts and message;
  CLIP routes DWF and DGN underlays there; Enter at a corner asks again.
- The right-edge underlay tools show for DWF and DGN too (import is PDF
  only).
- Underlay layers: DGN levels (V8 level table, "Default" listed as "0"; V7
  used levels named from the level name table), hidden through the layer
  override data with the DGN placeholder string first; a plotted DWF has
  none.
- V8 colour read from its colour word (by level, index, or a true colour
  drawn as its nearest index); 3D V8 elements drawn in plan (lines, line
  strings, ellipses and arcs by their orientation, text); a model's extent
  includes its text.
- DWF 6 TrueType text (font, height, rotation from the font opcode) and DWFx
  glyph runs are drawn; the default W2D colour map is the measured one.
- Contrast pulls lightness towards a per-kind pivot as measured (PDF 0.5,
  DWF 0.243, DGN 0.65).
- Zoom extents includes raster images and underlays whose frames are hidden.

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

src/app/commands/blocks.rs

@@ -709,9 +709,14 @@ impl OpenCADStudio {
                     Err(_) => self.command_line.push_error(&format!("{path} not found.")),
                 }
             }
-            "PDFCLIP" => {
+            "PDFCLIP" | "DWFCLIP" | "DGNCLIP" => {
                 use crate::command::CadCommand;
-                let command = crate::modules::insert::pdf_clip::PdfClipCommand::new();
+                let kind = match cmd {
+                    "DWFCLIP" => codec::entities::UnderlayType::Dwf,
+                    "DGNCLIP" => codec::entities::UnderlayType::Dgn,
+                    _ => codec::entities::UnderlayType::Pdf,
+                };
+                let command = crate::modules::insert::pdf_clip::PdfClipCommand::for_kind(kind);
                 self.command_line.push_info(&command.prompt());
                 self.tabs[i].active_cmd = Some(Box::new(command));
             }