refactor: Update type annotation for query result in complete-upload route

src/app/api/complete-upload/route.ts

@@ -2,6 +2,7 @@ import { NextResponse } from 'next/server';
 import pool from '@/lib/db';
 import bcrypt from 'bcrypt';
 import crypto from 'crypto';
+import { ResultSetHeader } from 'mysql2/promise';
 
 const SALT_ROUNDS = 10;
 
@@ -28,7 +29,7 @@ export async function POST(request: Request) {
 
     const connection = await pool.getConnection();
     try {
-      const [result]: [{ affectedRows: number }, unknown] = await connection.query(
+      const [result]: [ResultSetHeader, unknown] = await connection.query(
         'UPDATE files SET token_hash = ?, expires_at = ? WHERE id = ?',
         [tokenHash, expiresAt, file_id]
       );