refactor: update Vercel configuration to use rewrites instead of routes

- Removed the builds and routes sections from vercel.json.
- Added a rewrites section to direct traffic to the API entry point.
- Cleaned up CORS headers configuration.

Author: missuo

vercel.json

@@ -1,34 +1,19 @@
 {
-  "version": 2,
-  "builds": [
-    {
-      "src": "api/entrypoint.go",
-      "use": "@vercel/go"
-    }
-  ],
-  "routes": [
-    {
-      "src": "/(.*)",
-      "dest": "/api/entrypoint.go"
-    }
-  ],
   "headers": [
     {
       "source": "/(.*)",
       "headers": [
         {
           "key": "Access-Control-Allow-Origin",
           "value": "*"
-        },
-        {
-          "key": "Access-Control-Allow-Methods",
-          "value": "GET, POST, PUT, DELETE, OPTIONS"
-        },
-        {
-          "key": "Access-Control-Allow-Headers",
-          "value": "Content-Type, Authorization"
         }
       ]
     }
+  ],
+  "rewrites": [
+    {
+      "source": "/(.*)",
+      "destination": "/api/entrypoint.go"
+    }
   ]
 }