Add log directory configuration for macOS

[Wz58luck]

This pull request introduces a user-configurable log directory for the Lithe macOS app, allowing users to view, set, and restore the directory where logs are saved. The changes include updates to the settings model, UI enhancements in the settings view, new persistence logic, and comprehensive tests to ensure correct behavior. Additionally, a requirements specification document has been added to clarify the scope and acceptance criteria for this feature.

Log Directory Customization

• Added a new customLogDirectory property to AppSettings, with logic to persist, restore, and reset the custom log directory. The effective log directory is now determined by this setting, defaulting to the standard user logs location if unset. (Sources/Lithe/Models/Settings/AppSettings.swift) [1] [2] [3] [4] [5]
• Updated the settings UI to display both the default and current log directories, allow users to select a custom directory, restore the default, and copy directory paths. (Sources/Lithe/Views/App/SettingsView.swift) [1] [2] [3]

Testing and Documentation

• Added a test to verify that the custom log directory persists across app launches and can be restored to default, ensuring robust behavior. (Tests/LitheTests/AppSettingsTests.swift)
• Introduced a requirements specification document detailing the motivation, scope, UI/UX, and acceptance criteria for the macOS log directory configuration feature. (docs/superpowers/specs/2026-08-17-cross-platform-logging-requirements.md)

测试前后对比图

[xiaoyumuxi]

基本没啥问题了