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/modules/insert/mod.rs

@@ -105,7 +105,28 @@ impl CadModule for InsertModule {
                     tools: vec![
                         RibbonItem::LargeTool(mview_block::tool()),
                         RibbonItem::LargeTool(insert_block::tool()),
-                        RibbonItem::LargeTool(attedit::tool()),
+                        RibbonItem::LabeledDropdown {
+                            id: "ATTEDIT_DROPDOWN",
+                            label: "Edit Attribute",
+                            icon: attedit::ICON,
+                            items: vec![
+                                ("ATTEDIT", "Single", attedit::ICON),
+                                ("-ATTEDIT", "Multiple", attedit::ICON),
+                            ],
+                            default: "ATTEDIT",
+                        },
+                        // ATTMODE: the face shows the drawing's current setting.
+                        RibbonItem::LabeledDropdown {
+                            id: "ATTMODE_DROPDOWN",
+                            label: "",
+                            icon: attedit::ICON,
+                            items: vec![
+                                ("ATTMODE1", "Retain Attribute Display", attedit::ICON),
+                                ("ATTMODE2", "Display All Attributes", attedit::ICON),
+                                ("ATTMODE0", "Hide All Attributes", attedit::ICON),
+                            ],
+                            default: "ATTMODE1",
+                        },
                     ],
                 },
                 // ── Block Definition (slide-out: Set Base Point, Synchronize) ─────