fix: add BigInt JSON serialization patch for Prisma BigInt columns

UploadedFile.sizeBytes is BigInt → JSON.stringify throws TypeError.
Add BigInt.prototype.toJSON to convert to Number globally.

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

src/main.ts

@@ -1,3 +1,6 @@
+// Patch BigInt JSON serialization (Prisma returns BigInt for BigInt columns)
+;(BigInt.prototype as any).toJSON = function () { return Number(this) };
+
 import { NestFactory } from '@nestjs/core';
 import { SwaggerModule, DocumentBuilder } from '@nestjs/swagger';
 import { AppModule } from './app.module';