fix: Windows 托盘跟随系统读取区域设置

[ByteColtX]

Summary

• Read the Windows user default locale name for tray System language selection.
• Keep POSIX locale environment variables as fallback.
• Add locale resolution coverage for zh-CN, en-US, unknown fallback, and explicit preference overrides.

Tests

• cargo test i18n --lib
• cargo test
• cargo clippy --all-targets -- -D warnings
• RC_PATH=/usr/bin/true cargo check --target x86_64-pc-windows-msvc

Closes #12