Accept DB_DATABASE (Coolify convention) in addition to DB_NAME

Coolify auto-injected env vars from an attached Postgres use DB_DATABASE,
but the cotizador code read DB_NAME. Now both are accepted (DB_DATABASE
takes priority) across db.ts, seed.ts, and prisma.config.ts so attaching a
managed Postgres in Coolify Just Works.

prisma/seed.ts

@@ -7,7 +7,7 @@ const adapter = new PrismaPg({
   port: parseInt(process.env.DB_PORT || "5432"),
   user: process.env.DB_USER || "postgres",
   password: process.env.DB_PASSWORD || "postgres",
-  database: process.env.DB_NAME || "cotizador_e3",
+  database: process.env.DB_DATABASE || process.env.DB_NAME || "cotizador_e3",
 });
 const prisma = new PrismaClient({ adapter });