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">