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/components/providers.tsx

@@ -0,0 +1,29 @@
+"use client";
+
+import { ThemeProvider } from "next-themes";
+import { Toaster } from "@/components/ui/sonner";
+import { TooltipProvider } from "@/components/ui/tooltip";
+import { I18nProvider, type Locale } from "@/lib/i18n/provider";
+import en from "@/messages/en.json";
+import fr from "@/messages/fr.json";
+
+const messages = { en, fr } as Record<string, Record<string, unknown>>;
+
+export function Providers({
+  children,
+  initialLocale,
+}: {
+  children: React.ReactNode;
+  initialLocale?: Locale;
+}) {
+  return (
+    <ThemeProvider attribute="class" defaultTheme="system" enableSystem>
+      <I18nProvider messages={messages} initialLocale={initialLocale}>
+        <TooltipProvider>
+          {children}
+          <Toaster richColors position="top-right" />
+        </TooltipProvider>
+      </I18nProvider>
+    </ThemeProvider>
+  );
+}