feat(frontend): add shared client libraries and UI primitives

Introduce API helpers, types, hooks, design-system components, and the authenticated app shell.

frontend/src/components/providers.tsx

@@ -0,0 +1,25 @@
+"use client";
+
+import React from "react";
+import { MotionConfig } from "framer-motion";
+import { QueryClientProvider } from "@tanstack/react-query";
+import { ThemeProvider } from "next-themes";
+import { Toaster, toast } from "sonner";
+import { ErrorBoundary } from "@/components/error-boundary";
+import { queryClient } from "@/lib/query-client";
+import { softTween } from "@/lib/motion";
+
+export function Providers({ children }: { children: React.ReactNode }) {
+  return (
+    <QueryClientProvider client={queryClient}>
+      <ThemeProvider attribute="class" defaultTheme="dark" enableSystem={false}>
+        <MotionConfig reducedMotion="user" transition={softTween}>
+          <ErrorBoundary area="app">{children}</ErrorBoundary>
+        </MotionConfig>
+        <Toaster position="top-center" richColors closeButton />
+      </ThemeProvider>
+    </QueryClientProvider>
+  );
+}
+
+export { toast };