Add Next.js client app with Prisma and auth

Introduce a new 'client' Next.js app scaffold: configuration files (next.config.ts, eslint.config.mjs, postcss, tsconfig), Prisma config and schema, app routes including NextAuth API and server actions, session/provider utilities, proxy, public assets, README and .gitignore. Also add IDE project files under .idea and a root README to initialize the repository structure for development.

client/prisma.config.ts

@@ -0,0 +1,14 @@
+// This file was generated by Prisma, and assumes you have installed the following:
+// npm install --save-dev prisma dotenv
+import "dotenv/config";
+import { defineConfig } from "prisma/config";
+
+export default defineConfig({
+  schema: "prisma/schema.prisma",
+  migrations: {
+    path: "prisma/migrations",
+  },
+  datasource: {
+    url: process.env["DATABASE_URL"],
+  },
+});