The uploadFile callback was converting images to data URLs via FileReader,
which caused images to get stuck on "Loading..." in the editor. Switched
to URL.createObjectURL() which returns a lightweight blob URL immediately.
The Tauri vault-save path is now fully fire-and-forget so it never blocks
the URL return.
Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>