forked from 1b-agent/opencadstudio-upstream
Wire up save for the web build: - `io::save_to_bytes`: serialize a document to a byte buffer (DXF via write_to_vec, DWG via write_to_writer over a Cursor). - `io::download_web`: browser save dialog → write bytes (triggers a download). - Save and Save As on wasm both go through a new `web_save` helper: serialize the active tab and offer a download (no persistent path or in-app save dialog on the web). Format follows the tab name's extension, defaulting to DWG. Result reported via `WebSaveResult`. Native build + 75 tests unchanged. Co-Authored-By: Claude Opus 4.8 <[email protected]>