Switch to prisma-client-js generator to fix Turbopack RSC crash

The new prisma-client generator outputs TypeScript files to src/generated/prisma/
which include import.meta.url at module level. Turbopack sees this and marks the
entire module as a client reference, causing 'Cannot access toStringTag on the
server' on every page that uses Prisma.

Switching to prisma-client-js puts the generated client in node_modules/@prisma/client
where serverExternalPackages can properly exclude it from the server bundle.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

prisma/schema.prisma

@@ -1,6 +1,5 @@
 generator client {
-  provider = "prisma-client"
-  output   = "../src/generated/prisma"
+  provider = "prisma-client-js"
 }
 
 datasource db {

src/lib/prisma.ts

@@ -1,4 +1,4 @@
-import { PrismaClient } from "@/generated/prisma/client";
+import { PrismaClient } from "@prisma/client";
 import { PrismaPg } from "@prisma/adapter-pg";
 
 const globalForPrisma = globalThis as unknown as {