chore: migrate to PostgreSQL with Prisma

lib/prisma.ts

@@ -0,0 +1,15 @@
+import { PrismaClient } from "@prisma/client";
+
+const globalForPrisma = globalThis as unknown as {
+  prisma: PrismaClient | undefined;
+};
+
+export const prisma =
+  globalForPrisma.prisma ??
+  new PrismaClient({
+    // In Prisma 7, the connection URL should ideally come from prisma.config.ts
+    // or passed here if not using the new config system.
+    // For now, let's see if it picks up the URL automatically.
+  });
+
+if (process.env.NODE_ENV !== "production") globalForPrisma.prisma = prisma;