feat: Next.js + Tailwind + shadcn/ui project skeleton

- create-next-app with TypeScript, App Router, Tailwind CSS
- shadcn/ui initialized with defaults (button component + utils)
- .env.example with DATABASE_URL and SESSION_SECRET placeholders
- README.md with docs/runbooks/ reference

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

lib/utils.ts

@@ -0,0 +1,6 @@
+import { clsx, type ClassValue } from "clsx"
+import { twMerge } from "tailwind-merge"
+
+export function cn(...inputs: ClassValue[]) {
+  return twMerge(clsx(inputs))
+}