style(theme): 优化SVG图标并新增暗色主题配置

- 优化了download、menu、minus-sign、plus、reply等SVG图标文件，移除了冗余的XML声明和命名空间
- 新增了6套暗色AI主题配置，包括琥珀流光、翡翠流光、翡翠森林、深海幽蓝、玫瑰绯红、紫罗兰梦
- 更新了README.md文档，改进了标题层级结构和命令说明章节
- 添加了详细的开发、构建、辅助命令说明和使用指南

cutejava-front/src/assets/icons/svg/add-file.svg

@@ -1 +1 @@
-<?xml version="1.0" standalone="no"?><!DOCTYPE svg PUBLIC "-//W3C//DTD SVG 1.1//EN" "http://www.w3.org/Graphics/SVG/1.1/DTD/svg11.dtd"><svg t="1608282937930" class="icon" viewBox="0 0 1044 1024" version="1.1" xmlns="http://www.w3.org/2000/svg" p-id="3606" xmlns:xlink="http://www.w3.org/1999/xlink" width="203.90625" height="200"><defs><style type="text/css"></style></defs><path d="M89.87901 88.295661h850.640308v423.715173h88.273994V60.208481a60.186814 60.186814 0 0 0-60.186814-60.186814H61.79183a60.186814 60.186814 0 0 0-61.791796 60.186814V963.010695a60.186814 60.186814 0 0 0 60.186814 60.186814h450.197371v-88.273994H89.87901z" p-id="3607"></path><path d="M259.204581 260.831196h499.951803v88.273994H259.204581zM1044.040638 751.153109h-181.362933V573.80263h-88.273995v177.350479H592.238286v88.273994h182.165424v177.350479h88.273995v-177.350479h181.362933v-88.273994z" p-id="3608"></path></svg>
+<svg class="icon" viewBox="0 0 1044 1024" xmlns="http://www.w3.org/2000/svg" width="203.906" height="200"><defs><style/></defs><path d="M89.879 88.296h850.64V512.01h88.274V60.208A60.187 60.187 0 0 0 968.606.022H61.792A60.187 60.187 0 0 0 0 60.208v902.803a60.187 60.187 0 0 0 60.187 60.187h450.197v-88.274H89.88z"/><path d="M259.205 260.831h499.951v88.274H259.205zm784.836 490.322H862.678v-177.35h-88.274v177.35H592.238v88.274h182.166v177.35h88.274v-177.35h181.363v-88.274z"/></svg>