REFACTOR(db): migrate from MySQL to PostgreSQL

- Update database configuration for PostgreSQL
- Change Prisma provider from mysql to postgresql

nextjs/prisma/schema.prisma

@@ -7,7 +7,7 @@ generator client {
 }
 
 datasource db {
-  provider = "mysql"
+  provider = "postgresql"
   url      = env("DATABASE_URL")
 }