FIELD: Field dialog, FIELD command and the ATTDEF field buttons

A Field dialog with the fields the application evaluates and the
reference format choices, FIELD placing a field as multi-line text, the
attribute definition dialogs' field buttons, field attachment on commit,
system variable / file size / regional date providers for field
evaluation, and the codec patch with the field authoring API.

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

src/app/update/mod.rs

@@ -1813,6 +1813,7 @@ impl OpenCADStudio {
 
             Message::PdfDialog(message) => self.update_pdf_dialog(message),
             Message::AttdefDialog(message) => self.on_attdef_dialog(message),
+            Message::FieldDialog(message) => self.on_field_dialog(message),
             Message::PcManager(message) => self.update_pc_manager(message),
             Message::RibbonSelectTab(idx) => {
                 self.ribbon.select(idx);
@@ -8503,6 +8504,10 @@ impl OpenCADStudio {
             }
 
             Message::CloseModal => {
+                if self.active_modal == Some(super::ModalKind::Field) {
+                    self.close_field_dialog();
+                    return Task::none();
+                }
                 if matches!(
                     self.active_modal,
                     Some(super::ModalKind::AttDef | super::ModalKind::AttDefEdit)