Xref attach: Attach dialog, reference prompts, and xref drawings other applications can open

Attach External Reference dialog after XATTACH / ATTACH; ATTACH routes
drawings, PDFs and images; placement prompts and messages follow the
reference (presets, Corner/XYZ, nonzero check, existing definition reuse,
missing file, self-reference); name keeps the file's case; overlay and
path type at attach; one undo step for definition and INSERT; -XREF option
prompt and `?` table; XREF opens the palette; ER alias; xref Properties
rows; dependent symbols flagged and remapped and resolved content left out
of the saved file; dialog_ok automation action; localized labels.

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

src/app/update/file.rs

@@ -2105,7 +2105,8 @@ impl OpenCADStudio {
         }
 
         let mut recent_task = Task::none();
-        let saved = match crate::io::save_to_bytes(&self.tabs[i].scene.document, &ext, version) {
+        let document = self.tabs[i].scene.document_for_save();
+        let saved = match crate::io::save_to_bytes(&document, &ext, version) {
             Ok(bytes) => {
                 crate::sys::download_bytes(&filename, &bytes);
                 let cache_name = std::path::Path::new(&filename)