feat(web): Next.js 15 app shell, auth, i18n, base UI

App Router setup with next-intl (en/fr), Better Auth wiring, shadcn/ui components,
Tailwind, AES-256-GCM encrypt util, Redis rate limiter, tier limit checker,
site_settings helper for runtime .env overrides.

apps/web/next.config.ts

@@ -0,0 +1,7 @@
+import type { NextConfig } from "next";
+
+const nextConfig: NextConfig = {
+  /* config options here */
+};
+
+export default nextConfig;