feat: 添加品牌 Logo、favicon、Apple Touch Icon 和 OG 分享图

- 新增 icon.png (96x96) 和 apple-icon.png (180x180) 作为浏览器/iOS 图标
- 新增 opengraph-image.png 用于微信等社交媒体分享预览
- 新增 BrandLogo SVG 组件，首页标题上方展示品牌图标

src/app/page.tsx

@@ -7,6 +7,7 @@ import { Plus, LogIn, Loader2, MapPin, Navigation, X, Users, Heart, Sparkles, Ch
 import { getUserId, getCachedProfile, getCachedPreferences } from "@/lib/userId";
 import { getAvatarBg } from "@/lib/avatars";
 import AuthModal from "@/components/AuthModal";
+import BrandLogo from "@/components/BrandLogo";
 import { SCENES, getSceneConfig } from "@/lib/sceneConfig";
 import type { UserProfile, SceneType } from "@/types";
 
@@ -283,7 +284,8 @@ export default function LandingPage() {
         animate={{ y: 0, opacity: 1 }}
         transition={{ duration: 0.5 }}
       >
-        <h1 className="text-3xl font-black tracking-tight text-zinc-900">
+        <BrandLogo size={56} />
+        <h1 className="mt-2.5 text-3xl font-black tracking-tight text-zinc-900">
           NoWhatever
         </h1>
         <p className="mt-0.5 text-sm font-medium tracking-widest text-zinc-400">

src/components/BrandLogo.tsx

@@ -0,0 +1,37 @@
+export default function BrandLogo({ size = 48 }: { size?: number }) {
+  return (
+    <svg
+      width={size}
+      height={size}
+      viewBox="0 0 120 120"
+      fill="none"
+      xmlns="http://www.w3.org/2000/svg"
+      role="img"
+      aria-label="NoWhatever"
+    >
+      <rect width="120" height="120" rx="28" fill="url(#logo-grad)" />
+
+      {/* Tilted card */}
+      <g transform="translate(60,56) rotate(-15)">
+        <rect x="-26" y="-32" width="52" height="64" rx="7" fill="white" />
+      </g>
+
+      {/* Fork */}
+      <g transform="translate(48,50) rotate(-15)" fill="white" opacity="0.92">
+        <path d="M-4,-14 L-4,-4 Q-4,0 0,0 Q4,0 4,-4 L4,-14 M-4,-14 L-4,-20 M4,-14 L4,-20 M0,-14 L0,-20 M0,0 L0,10" stroke="#10b981" strokeWidth="2.5" strokeLinecap="round" fill="none" />
+      </g>
+
+      {/* Heart */}
+      <g transform="translate(72,52) rotate(-15)">
+        <path d="M0,4 Q0,0 -4,-2 Q-8,-4 -8,0 Q-8,4 0,10 Q8,4 8,0 Q8,-4 4,-2 Q0,0 0,4Z" fill="#10b981" opacity="0.85" />
+      </g>
+
+      <defs>
+        <linearGradient id="logo-grad" x1="0" y1="0" x2="120" y2="120" gradientUnits="userSpaceOnUse">
+          <stop stopColor="#34d399" />
+          <stop offset="1" stopColor="#059669" />
+        </linearGradient>
+      </defs>
+    </svg>
+  );
+}