Add Simplified Chinese localization for UI-TARS Desktop

[714307168]

Title: Add Simplified Chinese localization for UI-TARS Desktop

Summary:

• Add a lightweight renderer-side i18n helper with English and Simplified Chinese strings.
• Localize the main home page, local operator page, sidebar, settings dialogs, VLM settings, and confirmation dialogs.
• Use Chinese automatically when the stored language is zh or the browser/system language starts with zh; English remains the fallback.

Validation:

• corepack pnpm --filter ui-tars-desktop typecheck
• corepack pnpm --filter ui-tars-desktop build with UI_TARS_APP_PRIVATE_KEY_BASE64 set for local build

Notes:

• This is a first pass over the primary desktop UI surfaces. Some secondary/share/preset screens still contain English and can be localized in follow-up PRs.

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