Add Antigravity usage support

[trent-hord]

This pull request adds support for Google Antigravity usage monitoring across the app, including updates to the documentation and localization files for all supported languages. Users can now enable Antigravity as a provider alongside Claude Code and Codex, and the app will display Antigravity usage bars, tray icons, and handle authentication status for Antigravity accounts.

Major new provider support:

• Added Google Antigravity as an optional provider throughout the app, including usage bars, tray icon, and authentication handling. [1] [2] [3] [4] [5] [6]

Localization updates:

• Added antigravity_model, antigravity_token_expired_title, antigravity_token_expired_body, and antigravity_window_title strings to all supported languages (english.rs, dutch.rs, french.rs, german.rs, japanese.rs, korean.rs, portuguese_brazil.rs, russian.rs, spanish.rs, traditional_chinese.rs). [1] [2] [3] [4] [5] [6] [7] [8] [9] [10] [11] [12] [13] [14] [15] [16] [17] [18] [19]

Codebase organization:

• Fixed the module import order in mod.rs to keep all language modules organized.
• Extended the Strings struct to include the new Antigravity-related fields. [1] [2]

These changes ensure that Antigravity is now a first-class provider in the widget, with full multi-language support and user-facing documentation.