Add CardNav, theme providers, and UI updates

Introduce an interactive top navigation and theming + site UI/branding changes.

- Add CardNav component (TSX + CSS) with GSAP animations and responsive behavior.
- Dynamic Header now loads CardNav (client-side).
- Add Providers (next-themes) and wrap RootLayout; enable theme toggle and update site title to "Koring Team".
- Add Koring logo component and public SVG asset.
- Add custom 404 (app/not-found.tsx).
- Update home page spacing and card paddings for responsiveness.
- Refactor Footer content and layout for legal/branding text.
- Add dependencies: gsap, react-icons and update pnpm lock.

app/not-found.tsx

@@ -0,0 +1,26 @@
+import Link from "next/link";
+import { Button } from "@/components/ui/button";
+import { FlickeringGrid } from "@/components/ui/flickering-grid";
+
+export default function NotFound() {
+  return (
+    <div className="relative flex flex-col items-center justify-center min-h-[60vh] gap-6" style={{ height: "85vh" }}>
+      <FlickeringGrid
+        className="absolute inset-0 z-0 mask-[radial-gradient(700px_circle_at_center,white,transparent)]"
+        squareSize={6}
+        gridGap={14}
+        color="#6b9eb6"
+        maxOpacity={0.7}
+        flickerChance={0.1}
+      />
+      <div className="relative z-10 flex flex-col items-center gap-2">
+        <span className="text-8xl font-black tracking-tighter text-muted-foreground/20">404</span>
+        <h1 className="text-2xl font-bold">页面未找到</h1>
+        <p className="text-sm text-muted-foreground">你访问的页面不存在或已被移除</p>
+      </div>
+      <Link href="/" className="relative z-10">
+        <Button>返回首页</Button>
+      </Link>
+    </div>
+  );
+}