Attach Underlay ribbon menu, DWF/DGN attach dialog, DGN true colours

- Insert > Reference: the PDF Attach button becomes an Attach Underlay menu
  (PDF / DWF / DGN); its face runs the last one chosen.
- DWFATTACH, DGNATTACH and ATTACH on a .dwf/.dwfx/.dgn open the Attach
  dialog for that kind: sheets or models with thumbnails (one chosen),
  placement, path type, file details with the sheet / model size, and for
  DGN the conversion units (sub units offer 1 / sub units per master as the
  scale).
- DGN V8 true colours come from the ExtendedColors record packed in the
  non-model attributes stream; the colour word's high part numbers them.
- A DGN model's extent includes each text's box (its length along the
  baseline and 1.5 x its height), as the reference sizes a model.
- DWFx text uses the family named in its embedded (deobfuscated) font.
- DWF contrast pivots at 0.73 once colours are turned over for a dark
  background.
- Hairline strokes are drawn solid one pixel wide, and underlay rasters are
  made at or below their size on screen so those lines stay unbroken.

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

src/app/view/modal.rs

@@ -24,7 +24,11 @@ impl OpenCADStudio {
             Some(K::LayerTranslator) => crate::t!("Layer Translator").into_owned(),
             Some(K::DrawingUnits) => crate::t!("Drawing Units").into_owned(),
             Some(K::BlockDefinition) => crate::t!("Block Definition").into_owned(),
-            Some(K::PdfAttach) => crate::t!("Attach PDF Underlay").into_owned(),
+            Some(K::PdfAttach) => match self.pdf_attach.as_ref().map(|s| s.kind) {
+                Some(codec::entities::UnderlayType::Dwf) => crate::t!("Attach DWF Underlay").into_owned(),
+                Some(codec::entities::UnderlayType::Dgn) => crate::t!("Attach DGN Underlay").into_owned(),
+                _ => crate::t!("Attach PDF Underlay").into_owned(),
+            },
             Some(K::UnderlayLayers) => crate::t!("Underlay Layers").into_owned(),
             Some(K::PdfImportSettings) => crate::t!("PDF Import Settings").into_owned(),
             Some(K::PdfImportFile) => crate::t!("Import PDF").into_owned(),