fix: add xorg.libxkbfile dependency to resolve native-keymap runtime error

[boheastill]

Summary

This PR adds xorg.libxkbfile to the FHS environment dependencies.
It appears that Antigravity utilizes the native-keymap Electron module, which depends on libxkbfile. This is evidenced by the runtime error logs observed when the library is missing.

Context & Bug Report

I ran the original flake using nix run github:jacopone/antigravity-nix.

Behavior:

1. The application launched successfully (GUI appeared).
2. However, the terminal logged the following error immediately:

Error: Cannot find module './build/Debug/keymapping'
Require stack:
- .../node_modules/native-keymap/index.js
...
TypeError: Cannot read properties of null (reading 'getCurrentKeyboardLayout')

This error indicates that the native-keymap module failed to load due to the missing libxkbfile.so shared library. This suggests that keyboard mapping functionality (provided by this module) might be impaired, although I did not explicitly test the mapping behavior itself.

Solution

Added xorg.libxkbfile to package.nix in the targetPkgs list.

Verification

• Build: Ran nix build . successfully.
• Runtime: Validated by running the built binary ./result/bin/antigravity.
• Result: The application launches, and the terminal log is now clean (no native-keymap errors), confirming that the dependency issue is resolved.

Appendix: System Configuration

The issue was reproduced and fixed on the following system:

• OS: NixOS 26.05.20251202.418468a (Yarara)
• Kernel: Linux 6.12.60
• Nix Version: 2.31.2
• Desktop Environment: GNOME

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🇨🇳 中文说明 (Chinese Translation)

摘要
本 PR 向 FHS 环境依赖中添加了 xorg.libxkbfile。
从报错日志来看，Antigravity 似乎使用了 native-keymap Electron 模块，而该模块依赖此库。

背景与排查
我执行 nix run github:jacopone/antigravity-nix 启动应用。

现象：

1. 应用成功启动，GUI 界面正常弹出。
2. 但终端立即打印报错日志：Error: Cannot find module './build/Debug/keymapping'...。

这表明 native-keymap 模块因缺少 libxkbfile.so 而加载失败。这可能导致键盘映射功能失效（尽管我没有专门验证映射功能本身，只观察到报错）。

验证

• 在 package.nix 添加依赖后，重新构建并运行。
• 结果：日志变干净了，不再有上述报错，证明依赖修复有效。

附录：系统配置

• 系统: NixOS 26.05 (Unstable/Yarara)
• 桌面: GNOME
• 内核: 6.12.60

[jacopone]

LGTM! Thanks so much