Fix wasm32 build: gate the font download and XREF open call sites

crate::network and the open crate are desktop-only, but the community-font
download (font_repo.rs) and the XREF row Open action call them
unconditionally, so cargo check --target wasm32-unknown-unknown fails on
main. Gate both; on the web download_fonts returns an error, since the web
build has no network client or fonts folder.

src/app/update/mod.rs

@@ -2482,6 +2482,7 @@ impl OpenCADStudio {
                             if is_dwg {
                                 return self.update(Message::OpenRecent(std::path::PathBuf::from(found)));
                             } else {
+                                #[cfg(not(target_arch = "wasm32"))]
                                 let _ = open::that_detached(&found);
                             }
                         } else {