feat: use icon.png as app icon on welcome screen and about dialog

src/renderer/assets.d.ts

@@ -0,0 +1,14 @@
+declare module '*.png' {
+  const src: string
+  export default src
+}
+
+declare module '*.svg' {
+  const src: string
+  export default src
+}
+
+declare module '*.ico' {
+  const src: string
+  export default src
+}

src/renderer/components/Icons.tsx

@@ -1,4 +1,5 @@
 import React from 'react'
+import appIconUrl from '../assets/icon.png'
 
 // 统一图标 Props
 interface IconProps {
@@ -9,31 +10,10 @@ interface IconProps {
 
 const defaultProps: Partial<IconProps> = { size: 18 }
 
-// ===== 应用图标（现代化简洁风格） =====
+// ===== 应用图标 =====
 export function AppIcon({ size = 80 }: IconProps) {
   return (
-    <svg width={size} height={size} viewBox="0 0 80 80" fill="none" xmlns="http://www.w3.org/2000/svg">
-      <defs>
-        <linearGradient id="app-bg" x1="0" y1="0" x2="0" y2="1">
-          <stop offset="0%" stopColor="#4F8EF7"/>
-          <stop offset="100%" stopColor="#2563EB"/>
-        </linearGradient>
-        <linearGradient id="app-highlight" x1="0" y1="0" x2="1" y2="1">
-          <stop offset="0%" stopColor="white" stopOpacity="0.15"/>
-          <stop offset="50%" stopColor="white" stopOpacity="0"/>
-        </linearGradient>
-      </defs>
-      {/* 圆角矩形背景 */}
-      <rect x="4" y="4" width="72" height="72" rx="16" fill="url(#app-bg)"/>
-      {/* 左上角高光 */}
-      <rect x="4" y="4" width="72" height="72" rx="16" fill="url(#app-highlight)"/>
-      {/* MD 文字 */}
-      <text x="40" y="46" textAnchor="middle" dominantBaseline="central"
-            fontFamily="Georgia, 'Times New Roman', serif" fontWeight="bold" fontSize="24"
-            fill="white" letterSpacing="1.5">MD</text>
-      {/* 底部装饰线 */}
-      <rect x="20" y="58" width="40" height="2.5" rx="1.25" fill="white" fillOpacity="0.25"/>
-    </svg>
+    <img src={appIconUrl} alt="MarkLite" width={size} height={size} draggable={false} />
   )
 }