DWF and DGN underlays: attach, display, snaps, frames and references

DWFATTACH / -DWFATTACH and DGNATTACH / -DGNATTACH attach a DWF / DWFx sheet
or a DGN (V7 or V8) model with the reference's prompts; ATTACH routes the
file types to them. The sheet or model is read into vector paths, drawn as a
transparent underlay raster (contrast, fade, monochrome and background
adjustment apply) and offers its geometry to object snaps. Definitions are
kept in ACAD_DWFDEFINITIONS / ACAD_DGNDEFINITIONS, the External References
palette lists and reloads them, and image textures get line-keeping mip
levels so thin underlay lines stay visible when zoomed out.

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

src/app/commands/styleprops.rs

@@ -1022,6 +1022,8 @@ impl OpenCADStudio {
                     | "DWFFRAME"
                     | "DGNFRAME"
                     | "PDFOSNAP"
+                    | "DWFOSNAP"
+                    | "DGNOSNAP"
                     | "UOSNAP"
                     | "PDFIMPORTMODE"
                     | "PDFIMPORTFILTER"
@@ -1181,7 +1183,9 @@ impl OpenCADStudio {
                         }
                         return Some(self.finish_dispatch(cmd));
                     }
-                    if matches!(name.as_str(), "PDFOSNAP" | "UOSNAP") {
+                    // ponytail: one flag for every underlay kind; split it if a drawing
+                    // needs PDF snaps on while DWF/DGN snaps are off.
+                    if matches!(name.as_str(), "PDFOSNAP" | "DWFOSNAP" | "DGNOSNAP" | "UOSNAP") {
                         let current = i16::from(crate::scene::model::pdf_vector::pdf_osnap());
                         if let Some(value) = &value {
                             match value.parse::<i16>().ok().filter(|value| (0..=1).contains(value)) {