Add support to download and load TTS model from ModelScope, with a fallback to the HuggingFace mirror.
Implement a `documentLoadStatus` property and helper functions in `office.js` to track file loading state.
Improve request cancellation logic in `api.js`, ensuring proper cancel URL resolution and request‑id handling.
These changes enhance robustness, reduce external dependencies, and provide better UX for office file handling.