fix(web): honor selected DWG/DXF version when saving

The web save path discarded the chosen format version (`let _ = version`)
and `save_to_bytes` never applied it, so every browser download was
written at the document's default version (AC1032 / DWG 2018) regardless
of the format picked in the Save dialog. (#122)

Thread `version` into `save_to_bytes` and set `doc.version` there, the
byte-buffer counterpart to `save_as_version`. Saving as DWG 2013 now
writes an AC1027 file.

Co-Authored-By: Claude Opus 4.8 <[email protected]>

src/app/update.rs

@@ -976,8 +976,7 @@ impl OpenCADStudio {
                 }
                 #[cfg(target_arch = "wasm32")]
                 {
-                    let _ = version;
-                    match crate::io::save_to_bytes(&self.tabs[i].scene.document, ext) {
+                    match crate::io::save_to_bytes(&self.tabs[i].scene.document, ext, version) {
                         Ok(bytes) => {
                             crate::sys::download_bytes(&filename, &bytes);
                             self.tabs[i].dirty = false;