Frames: state-following ribbon list, DWF/DGN frames, image frame encoding and profile, frame-only picking

- The Frames list shows the drawing's frame state (hide / display and plot /
  display but not plot / frames vary), follows commands, undo and document
  switches, and lists the mixed state as a disabled item.
- DWFFRAME and DGNFRAME are frame variables of their own, kept in the header,
  and FRAME sets them with the others.
- Out-of-range frame values say "Requires an integer between 0 and 2." and
  ask again; a set value reports "Regenerating model.".
- IMAGEFRAME is stored in the image variables as bits (2 is written as 3) and
  a drawing without them uses the profile value, which setting IMAGEFRAME
  updates and the settings file keeps.
- Raster images, PDF underlays and wipeouts are picked on their frame only;
  underlay snap geometry is never picked.

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

src/entities/underlay.rs

@@ -288,21 +288,20 @@ impl RenderConvertible for Underlay {
             });
         }
 
-        // Pick surface over the shown area so a click inside selects it.
-        let pick_ring: Vec<[f64; 3]> = if !clip.is_empty() && !self.clip_inverted {
+        // Picked on its frame only; the page itself selects nothing.
+        let key_ring: Vec<[f64; 3]> = if !clip.is_empty() && !self.clip_inverted {
             clip.clone()
         } else {
             quad.map(|q| q.to_vec()).unwrap_or_default()
         };
-        let pick_tris = crate::entities::mesh::triangulate_planar(&pick_ring);
         let mut snap_pts = vec![insertion_snap];
         snap_pts.extend(crate::scene::model::pdf_vector::underlay_snap_points(self, document));
         Some(RenderEntity {
-            pick_tris,
+            pick_tris: vec![],
             object: RenderObject::Lines(pts),
             snap_pts,
             tangent_geoms: vec![],
-            key_vertices: pick_ring,
+            key_vertices: key_ring,
             fill_tris: vec![],
         })
     }