Add Simplified Chinese (简体中文) to app language settings

Is your feature request related to a problem? Please describe.
The Claude desktop app's language settings currently do not include an option for Simplified Chinese (简体中文), even though many users primarily use Chinese to interact with Claude.

Describe the solution you'd like
Add "简体中文 (Simplified Chinese)" as a selectable UI language option in the app's language settings.

Additional context
This would improve the experience for Chinese-speaking users who want the app's own interface (not just Claude's responses) displayed in Simplified Chinese.