fix: 修复独立插件窗口重入未前置

[kuraxii]

fix: #503

变更内容

• 复用已存在的独立插件窗口时，显式调用 show() 后再执行 focus()
• 补充注释说明 macOS 下该处理的原因

[gemini-code-assist]

Code Review

This pull request updates the detached window management logic to ensure windows are properly brought to the foreground on macOS by calling show() before focus(). The reviewer suggested refining this implementation to avoid redundant calls when a window is minimized and to limit the show() call specifically to the macOS platform to prevent potential side effects on other systems.