feat(client): Implement Update Notifications and Fix IME Input

[rcyw]

Summary

This PR enhances the client application by introducing a manual update notification system and fixing a critical bug in the chat input related to IME (Input Method Editor) handling.

Changes

✨ Features

• Update Notification System:
  • A new hook useUpdateCheck periodically checks the GitHub Releases API for new versions.
  • When a new version is detected, a toast notification is displayed, allowing the user to download it or dismiss the notification.
  • An "About" section has been added to the Settings panel, showing the current app version and providing a manual "Check for Updates" button.
  • A detailed design document (docs/design/client-update-check.md) has been added to explain the rationale behind this manual approach and outline the future migration path to full in-app auto-updates.

🐛 Bug Fixes

• Chat Input IME Guard:
  • Implemented a useImeEnterGuard hook to correctly handle the Enter key during IME composition. This prevents the chat message from being sent accidentally while the user is typing in languages like Chinese, Japanese, or Korean.

housekeeping

• Dependency Cleanup: Removed the unused @tauri-apps/plugin-updater package, as the new implementation provides a temporary, more suitable solution for the current alpha stage.
• Version Correction: Corrected the app version in tauri.conf.json from 0.1.0 to 0.0.1.

How to Test

1. Run the client application.
2. Open the settings panel to view the new "About" section. Click "Check for updates".
3. Go to the chat input. Switch to a Pinyin/Japanese/Korean keyboard.
4. Type some characters (e.g., "nihao"). While the IME selection window is open, press Enter.
5. Expected: The text should be confirmed in the input box, but the message should NOT be sent.
6. Press Enter again.
7. Expected: The message should now be sent.