Feature Request: Auto-restore the last opened script on launch, and improve Chinese support (input, word tracking, and UI localization)

### Feature Request 1: Restore last opened file on launch

**Problem:** Every time I launch Textream from the Dock (not by double-clicking a .textream file), it opens a blank "Untitled" editor. My previously saved scripts are never auto-loaded, so I have to press ⌘O and navigate to the file every single time. This is very disruptive for a teleprompter workflow, where you often quit and relaunch the app between takes.

**Suggested implementation:**
- Persist `currentFileURL` to `UserDefaults` in `saveToURL` / `openFileAtURL` (e.g. key `lastOpenedFileURL`), and restore it on app launch — either by auto-opening it or by pre-filling the editor.
- Alternative: on launch, check `NSDocumentController.shared.recentDocumentURLs` and load the most recent `.textream` file.
- A setting toggle like "Restore last script on launch" (on by default) would be a nice touch.

### Feature Request 2: Chinese (Simplified) support — input, word tracking, and UI localization

**Problem:** As a Chinese user, I currently face three blockers:

1. **Cannot type Chinese in the editor.** I can only paste Chinese text in; direct Chinese IME input doesn't work properly (related to #34).
2. **Word Tracking / Voice-Activated modes are broken for Chinese text** (#60). This is the killer feature for Chinese streamers and presenters, and it's unusable for us right now.
3. **UI is English-only.** There is no Simplified Chinese localization.

These three issues together show that the Chinese-speaking user base is real but underserved. A Simplified Chinese localization, plus fixing CJK word tracking and IME input, would make Textream the go-to teleprompter for Chinese users.

For context, I'd love to recommend this app to friends, but the current state makes it hard.

Thanks for the great app — it's genuinely the nicest free teleprompter on macOS!