feat: 换用官方 logo 原图

- S 标从 2048 原图裁切：导航/页脚/admin 用 512 webp（96KB），favicon 32/64 圆角 png，apple-touch-icon 180
- OG 分享图用完整版 logo-full.jpg（含字标），index.html 补 og:title/description/image
- 自绘 SVG logo 退役；原图 8.4MB 移入 design-assets/（已 gitignore，不进构建产物）
- web/dist 总体积 1.0MB

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

web/src/components/logo.tsx

@@ -3,55 +3,17 @@ interface LogoMarkProps {
   className?: string
 }
 
-/** 品牌 Logo：霓虹数据流 S（青→蓝→紫），深岩底方形 */
+/** 品牌 Logo：霓虹数据流 S（用户原版位图裁切，源图在 design-assets/） */
 export function LogoMark({ size = 28, className }: LogoMarkProps) {
   return (
-    <svg
+    <img
+      src="/brand/logo-mark.webp"
       width={size}
       height={size}
-      viewBox="0 0 64 64"
-      className={className}
+      alt=""
       aria-hidden="true"
-    >
-      <defs>
-        <linearGradient id="logo-g" x1="0" y1="0" x2="1" y2="1">
-          <stop offset="0" stopColor="#34E5E0" />
-          <stop offset="0.5" stopColor="#3B82F6" />
-          <stop offset="1" stopColor="#A855F7" />
-        </linearGradient>
-      </defs>
-      <rect width="64" height="64" rx="14" fill="#0B1117" />
-      <g fill="none" strokeLinecap="round">
-        <path
-          d="M22 15 C41 15 41 31 32 32 C23 33 23 49 42 49"
-          stroke="url(#logo-g)"
-          strokeWidth="9"
-          opacity="0.22"
-        />
-        <path
-          d="M22 15 C41 15 41 31 32 32 C23 33 23 49 42 49"
-          stroke="url(#logo-g)"
-          strokeWidth="6"
-          opacity="0.45"
-        />
-        <path
-          d="M22 15 C41 15 41 31 32 32 C23 33 23 49 42 49"
-          stroke="url(#logo-g)"
-          strokeWidth="3.6"
-        />
-      </g>
-      <g fill="#34E5E0">
-        <circle cx="15" cy="13" r="1.4" />
-        <circle cx="10" cy="17" r="1" />
-        <circle cx="14" cy="20" r="0.8" />
-      </g>
-      <g stroke="#A855F7" strokeWidth="0.9" opacity="0.75">
-        <path d="M42 49 L50 46 M42 49 L53 51 M50 46 L53 51" fill="none" />
-      </g>
-      <g fill="#C084FC">
-        <circle cx="50" cy="46" r="1.5" />
-        <circle cx="53" cy="51" r="1.2" />
-      </g>
-    </svg>
+      className={className}
+      style={{ borderRadius: '22%' }}
+    />
   )
 }