Add shebang, fix compatibility with Prisma 5.7.0

The main script was missing a shebang, which caused it not to work with
several package manager and/or OS combinations. This adds that in, which
should fix the issues.

Additionally, the 5.7.0 version of @prisma/generator-helper no longer
seems to support named imports when importing from an ESM package, so
this switches to using the default export.

generator.ts

@@ -1,7 +1,12 @@
-import { DMMF, generatorHandler } from "@prisma/generator-helper";
+#!/usr/bin/env node
+import type { DMMF } from "@prisma/generator-helper";
+import generatorHelper from "@prisma/generator-helper";
 import { mkdir, writeFile } from "node:fs/promises";
 import { dirname } from "node:path";
 
+// Need to use default export for ESM compatibility
+const { generatorHandler } = generatorHelper;
+
 interface Config {
   enumPrefix: string;
   enumSuffix: string;