桌面应用图标替换为 B-brackets 设计（深藏青 + 白/蓝花括号）

- icon.svg 取自 opsx-icon-options/api/B-brackets.svg，全套光栅重生成：
  icon.icns（iconutil）、icon.ico（PNG-in-ICO 6 尺寸）、16-1024 PNG、Windows Square*/StoreLogo
- 替换 Tauri 脚手架默认五角星图标；GUI 重启实测 Dock 图标已生效
- 服务全量重启：server 8787（官网/文档 200）+ web 5173 + 桌面 GUI

apps/desktop/src-tauri/icons/icon.svg

@@ -1,13 +1,5 @@
-<?xml version="1.0" encoding="UTF-8"?>
 <svg xmlns="http://www.w3.org/2000/svg" width="512" height="512" viewBox="0 0 512 512">
-  <defs>
-    <linearGradient id="g" x1="0" y1="0" x2="1" y2="1">
-      <stop offset="0%" stop-color="#0B182C"/>
-      <stop offset="100%" stop-color="#0F203A"/>
-    </linearGradient>
-  </defs>
-  <rect x="28" y="28" width="456" height="456" rx="110" fill="url(#g)"/>
-  <text x="256" y="240" text-anchor="middle" font-family="SF Pro Display, Helvetica, Arial" font-size="140" font-weight="700" fill="#FFFFFF">API</text>
-  <text x="256" y="340" text-anchor="middle" font-family="SF Pro Display, Helvetica, Arial" font-size="42" fill="#94A3B8">Opsx</text>
-  <circle cx="110" cy="400" r="16" fill="#10B981"/>
+  <rect width="512" height="512" rx="112" fill="#0B182C"/>
+  <path d="M200 130c-48 0-70 28-70 70v28c0 22-14 34-34 38v20c20 4 34 16 34 38v28c0 42 22 70 70 70" fill="none" stroke="#FFFFFF" stroke-width="36" stroke-linecap="round"/>
+  <path d="M312 130c48 0 70 28 70 70v28c0 22 14 34 34 38v20c-20 4-34 16-34 38v28c0 42-22 70-70 70" fill="none" stroke="#3B82F6" stroke-width="36" stroke-linecap="round"/>
 </svg>