feat: 浏览器图标 — 蓝紫渐变圆角方块+白色盾牌勾选

frontend/index.html

@@ -3,6 +3,7 @@
   <head>
     <meta charset="UTF-8" />
     <meta name="viewport" content="width=device-width, initial-scale=1.0" />
+    <link rel="icon" type="image/svg+xml" href="/favicon.svg" />
     <title>SQL-Platform</title>
   </head>
   <body>

frontend/public/favicon.svg

@@ -0,0 +1,13 @@
+<svg xmlns="http://www.w3.org/2000/svg" width="64" height="64" viewBox="0 0 64 64">
+  <defs>
+    <linearGradient id="g" x1="0%" y1="0%" x2="100%" y2="100%">
+      <stop offset="0%" stop-color="#3b82f6"/>
+      <stop offset="100%" stop-color="#8b5cf6"/>
+    </linearGradient>
+  </defs>
+  <rect width="64" height="64" rx="14" fill="url(#g)"/>
+  <path d="M32 14 L48 22 L48 34 C48 44 40 50 32 54 C24 50 16 44 16 34 L16 22 Z" 
+        fill="none" stroke="white" stroke-width="2.5" stroke-linejoin="round"/>
+  <path d="M26 32 L30 36 L38 28" 
+        fill="none" stroke="white" stroke-width="2.5" stroke-linecap="round" stroke-linejoin="round"/>
+</svg>