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/app/update/mod.rs

@@ -326,9 +326,26 @@ impl OpenCADStudio {
         if self.tabs.get(self.active_tab).map(|tab| tab.id) != before {
             self.sync_underlay_tab();
         }
+        self.sync_frame_dropdown();
         task
     }
 
+    /// The Frames list on the ribbon shows the active drawing's frame state
+    /// (FRAME), however it was changed: the list, a command, undo or another
+    /// drawing.
+    fn sync_frame_dropdown(&mut self) {
+        let Some(tab) = self.tabs.get(self.active_tab).filter(|tab| !tab.is_start) else {
+            return;
+        };
+        let current = match crate::scene::frame::master_mode(&tab.scene.document) {
+            0 => "FRAMES0",
+            1 => "FRAMES1",
+            2 => "FRAMES2",
+            _ => "FRAMES3",
+        };
+        self.ribbon.set_dropdown_current("FRAMES_DROPDOWN", current);
+    }
+
     fn update_message(&mut self, msg: Message) -> Task<Message> {
         if let Some(tab) = self.tabs.get(self.active_tab) {
             crate::entities::common::set_unit_context(