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/commands/mod.rs

@@ -5,6 +5,7 @@ use iced::Task;
 use std::path::PathBuf;
 
 mod attdef;
+mod field;
 mod blocks;
 mod xref_attach;
 mod dim;
@@ -282,6 +283,9 @@ impl OpenCADStudio {
         if let Some(t) = self.dispatch_attdef(cmd, i) {
             return Some(t);
         }
+        if let Some(t) = self.dispatch_field(cmd, i) {
+            return Some(t);
+        }
         if let Some(t) = self.dispatch_draw(cmd, i) {
             return Some(t);
         }