fix PrismaService: pass datasources to PrismaClient constructor (required in v7)

backend/src/prisma/prisma.service.ts

@@ -3,6 +3,10 @@ import { PrismaClient } from '@prisma/client';
 
 @Injectable()
 export class PrismaService extends PrismaClient implements OnModuleInit, OnModuleDestroy {
+  constructor() {
+    super({ datasources: { db: { url: process.env.DATABASE_URL } } });
+  }
+
   async onModuleInit() {
     await this.$connect();
   }