Fix UTF-8 request body handling

vite.config.js

@@ -92,17 +92,19 @@ async function writeDatabase(data) {
 
 function readRequestBody(request) {
   return new Promise((resolve, reject) => {
-    let body = '';
+    const chunks = [];
+    let bodyLength = 0;
 
     request.on('data', (chunk) => {
-      body += chunk;
-      if (body.length > 5_000_000) {
+      chunks.push(chunk);
+      bodyLength += chunk.length;
+      if (bodyLength > 5_000_000) {
         reject(new Error('Request body is too large'));
         request.destroy();
       }
     });
 
-    request.on('end', () => resolve(body));
+    request.on('end', () => resolve(Buffer.concat(chunks).toString('utf8')));
     request.on('error', reject);
   });
 }