fix(ui): add a top-level renderer error boundary

[mrsibe]

What does this PR do?

Adds a top-level React error boundary so a render error can no longer leave the app as a blank window.

Why?

The renderer had no error boundary. Any render-phase exception made React unmount the whole tree, so the user got a white window with nothing to act on. The "Add to Note" crash (TypeError: ... reading 'getMarkdown' in NoteEditor) was the latest instance of this failure mode; the underlying crash is fixed separately, but the app should not be able to disappear like that again.

Related issue

None.

What changed?

• New AppErrorBoundary (src/renderer/src/components/common/AppErrorBoundary.tsx): catches render errors, logs the error and component stack via componentDidCatch, shows the error message and a Reload button.
• main.tsx wraps <App /> in the boundary.
• Added errorTitle, errorDescription and reload to the common namespace (en-US, zh-CN).

The boundary uses the i18n instance directly instead of useTranslation, because it must be able to render outside a React provider.

How was this tested?

• Temporarily made App throw during render, then launched npm run dev and inspected the window over Electron CDP:
  • window shows Something went wrong / An unexpected error occurred. Reload to continue. / the error message / Reload,
  • console shows [AppErrorBoundary] Uncaught render error: Error: ...,
  • the app stays interactive instead of blank.
• Reverted the temporary throw; only the boundary wiring remains.
• npm run typecheck:web passes.
• npm run check:design passes (no token/design violations).
• npx prettier --check on the touched files passes.

Screenshots / recordings

Not captured.

Checklist

• I have reviewed my own changes.
• npm run typecheck passes.
• npm run build passes.
• I have tested the affected user workflow.
• I have not included unrelated changes.
• I have updated documentation when necessary.

Desktop / build changes

• Not applicable