feat: in-app language switcher (English/Chinese) with full Chinese localization

[nailongooo99]

Summary

This PR adds an in-app language switcher to the home screen and introduces full
Simplified Chinese (zh-Hans) localization for the whole UI, so mond can be used
in either English or Chinese without an app restart.

What's included

• New "Language" section on the home screen (sibling to Logs / Tweaks) with a
  native segmented control, matching the style of the Exploit method picker in
  Settings, to switch between English and 中文.
• Instant, persistent switching: the selected language applies immediately to
  every view and is saved in UserDefaults, so it survives relaunches.
• Full Chinese localization of all user-facing strings: home screen, Settings
  (including every toggle description), MobileGestalt editor (tweak names, info
  popups, apply/revert/load alerts), CacheExtra editor, PosterBoard, Tendies
  explorer, HouseArrest file browser, and the startup "Not supported" alert.
• Context-aware translations using terms common in the Chinese jailbreak
  community (e.g. Respring → 注销, Tweaks → 插件, Stage Manager → 台前调度,
  Dynamic Island → 灵动岛), including fully translated long warnings such as
  the iPadOS Mode risk notice and the Apple Intelligence usage steps.

Design notes

• English strings in the codebase remain the source of truth. A lightweight
  L10n manager (mond/helpers/L10n.swift) resolves Chinese at runtime and falls
  back to English for any untranslated string.
• Since PartyUI components (PlainToggle, Alertinator, PlainAlert) take plain
  String rather than LocalizedStringKey, a small in-app localization manager is
  used instead of the system string catalog — this also enables switching
  without restarting the app.
• L10n is injected as an @EnvironmentObject so views re-render instantly on
  language change; L10n.shared is used for alerts and helper functions.

Testing

• Builds successfully (Release, unsigned IPA) with the existing GitHub Actions
  workflow.
• Installed and manually tested on a device: language switching works
  immediately, Chinese renders correctly throughout, and no regressions were
  observed in tweaks or settings.

Notes for maintainers

• The L10n layer is self-contained; it can be migrated to Xcode String Catalogs
  later if preferred.
• The Language section is placed at the top of the home list — easy to move if
  you'd prefer a different spot.