ATTDEF dialog error band and multi-line editor; ATTDISP sets ATTMODE

Validation messages show in the dialogs, the Default value of a multi-line
definition can be edited in the multi-line text editor, "Specify on-screen"
is kept for the session, ATTDISP sets ATTMODE with the reference prompt
instead of changing the definitions, and Insert > Block gets the Edit
Attribute (Single / Multiple) and attribute display lists.

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

src/app/update/mod.rs

@@ -344,6 +344,12 @@ impl OpenCADStudio {
             _ => "FRAMES3",
         };
         self.ribbon.set_dropdown_current("FRAMES_DROPDOWN", current);
+        let attmode = match tab.scene.document.header.attribute_visibility {
+            0 => "ATTMODE0",
+            2 => "ATTMODE2",
+            _ => "ATTMODE1",
+        };
+        self.ribbon.set_dropdown_current("ATTMODE_DROPDOWN", attmode);
     }
 
     fn update_message(&mut self, msg: Message) -> Task<Message> {