integrate backend Google OAuth and set up avatar media proxy

- Implement the full login and onboarding workflow to handle name, handle, and avatar.

- Rewrite avatar asset URLs to route through the self-hosted media service.

- Add Next.js rewrites configuration to proxy media requests directly to the FastAPI backend.

next.config.ts

@@ -2,6 +2,32 @@ import type { NextConfig } from "next";
 
 const nextConfig: NextConfig = {
   /* config options here */
+  images: {
+    remotePatterns: [
+      {
+        protocol: 'https',
+        hostname: 'lh3.googleusercontent.com',
+        port: '',
+        pathname: '/**',
+      },
+      {
+        protocol: 'http',
+        hostname: 'googleusercontent.com',
+        port: '',
+        pathname: '/**',
+      },
+    ],
+  },
+  async rewrites() {
+    return [
+      {
+        // 捕获所有以 /v1/media/ 开头的图片请求
+        source: '/v1/media/:path*',
+        // 悄悄转发给 FastAPI 后端
+        destination: `${process.env.NEXT_PUBLIC_API_URL || 'http://localhost:8000'}/v1/media/:path*`,
+      },
+    ];
+  },
 };
 
 export default nextConfig;