feat(app): add Simplified Chinese localization

[Chendeqisky]

PR title

feat(app): add Simplified Chinese localization

Summary

• add a generic Bundle-based lookup for runtime-provided SwiftUI labels
• package every app-owned .lproj directory while keeping English as the development language
• add a Simplified Chinese catalog for navigation, onboarding, settings, chat, Forge, benchmark, Hermes, and dynamic status text
• validate duplicate keys, format placeholders, and localization bundle wiring in CI

Validation

• swift build -c debug --product MTPLXApp
• swift test -c debug — 632 passed, 1 skipped
• pytest -q tests/test_app_localization.py — 2 passed
• plutil -lint Localizable.strings
• bash -n apps/MTPLXApp/script/build_and_run.sh
• direct Foundation lookup of static and formatted Simplified Chinese strings

Compatibility

• English remains the fallback and development language
• the app bundle identifier is unchanged
• Sparkle update behavior is unchanged
• additional languages can be added later by placing another .lproj directory under Resources/Localization