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/app/manifest.ts

@@ -0,0 +1,17 @@
+import type { MetadataRoute } from "next";
+
+export default function manifest(): MetadataRoute.Manifest {
+  return {
+    name: "Epicure",
+    short_name: "Epicure",
+    description: "Your AI-powered recipe book",
+    start_url: "/recipes",
+    display: "standalone",
+    background_color: "#ffffff",
+    theme_color: "#18181b",
+    icons: [
+      { src: "/icon-192.png", sizes: "192x192", type: "image/png" },
+      { src: "/icon-512.png", sizes: "512x512", type: "image/png" },
+    ],
+  };
+}