feat(field): Formula, Hyperlink and plot fields; local-time field dates, file times and display name; header dates on save

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

src/io/mod.rs

@@ -723,6 +723,7 @@ async fn load_web_bytes(
     }
     fix_viewport_status_flags(&mut doc);
     fix_current_style_names(&mut doc);
+    crate::entities::field::local_header_dates(&mut doc);
     progress.set(crate::app::OPEN_PHASE_CACHING, 7000, 0, 1);
     let dropped = purge_corrupt_entities(&mut doc);
     if !recovery_mode && dropped > 0 {
@@ -764,6 +765,7 @@ pub fn load_bytes(name: &str, bytes: Vec<u8>) -> Result<CadDocument, String> {
                 .map_err(|e| e.to_string())?;
             fix_viewport_status_flags(&mut doc);
             fix_current_style_names(&mut doc);
+    crate::entities::field::local_header_dates(&mut doc);
             Ok(doc)
         }
         "dxf" => {
@@ -775,6 +777,7 @@ pub fn load_bytes(name: &str, bytes: Vec<u8>) -> Result<CadDocument, String> {
             fix_dxf_layout_plot_settings(&mut doc);
             fix_viewport_status_flags(&mut doc);
             fix_current_style_names(&mut doc);
+    crate::entities::field::local_header_dates(&mut doc);
             Ok(doc)
         }
         _ => Err(format!("Unsupported file format: .{ext}")),
@@ -1040,6 +1043,7 @@ fn finalize_loaded_outcome(
     }
     fix_viewport_status_flags(doc);
     fix_current_style_names(doc);
+    crate::entities::field::local_header_dates(doc);
     resolve_raster_image_paths(doc, path.parent());
     doc.source_path = Some(path.to_string_lossy().into_owned());
     Ok(outcome)