Feature/windows screenshot feature improve

[Particaly]

Windows 平台截图预处理工具栏 — 实现了完整的截图后编辑功能，支持：

• 绘制工具：矩形、圆形、箭头、画笔、马赛克、文本
• 辅助功能：翻译（暂未接入）、撤销/重做
• 操作按钮：保存、取消、确认

1. 代码架构重构

• 将截图功能从 binding_windows.cpp 独立到 screenshot_windows.cpp
• 新增 StartRegionCapture 接口作为区域截图入口

2. 图标系统

• 新增 12 个 SVG 图标资源（src/assets/）
• 实现 gen-icons.js 构建脚本，将 SVG 转换为 C 头文件
• 支持运行时颜色替换，支持 normal/hover/active 三态

3. 第三方依赖

• 引入 nanosvg 库（nanosvg.h + nanosvgrast.h）用于 SVG 图标渲染

[gemini-code-assist]

Code Review

This pull request refactors the Windows region screenshot feature by moving its implementation out of src/binding_windows.cpp and introducing an automated SVG-to-C header generation script (scripts/gen-icons.js) to compile toolbar icons directly into the binary. It also adds several SVG assets and the nanosvgrast.h third-party library for SVG rasterization. Feedback on the changes points out that the toCLiteral function in scripts/gen-icons.js is defined but never used, suggesting its removal to clean up dead code.

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[gemini-code-assist]

在 scripts/gen-icons.js 中，函数 toCLiteral 被定义了但从未在代码中被调用。为了保持代码的整洁和可维护性，建议将这段未使用的死代码删除。