feat(frontend): implement TanStack Router with mobile sidebar

- Install and configure TanStack Router for type-safe routing
- Create route structure with __root.tsx layout and individual route files
- Implement mobile-responsive sidebar with collapse functionality
- Add clickable logo in sidebar that navigates to overview page
- Extract Header and Sidebar components from Dashboard for reusability
- Configure Vite with TanStack Router plugin for development
- Update main.tsx to use RouterProvider instead of direct App rendering
- Maintain existing TanStack Query integration seamlessly
- Add proper TypeScript types for all route components
- Implement responsive design with mobile overlay and hamburger menu

This replaces the tab-based navigation with URL-based routing while
maintaining the same user experience and adding powerful features like:
- Bookmarkable URLs (/transactions, /analytics, /notifications)
- Browser back/forward button support
- Direct linking capabilities
- Mobile-responsive sidebar with smooth animations
- Type-safe navigation with auto-completion

frontend/src/routes/analytics.tsx

@@ -0,0 +1,10 @@
+import { createFileRoute } from "@tanstack/react-router";
+
+export const Route = createFileRoute("/analytics")({
+  component: () => (
+    <div className="bg-white rounded-lg shadow p-6">
+      <h3 className="text-lg font-medium text-gray-900 mb-4">Analytics</h3>
+      <p className="text-gray-600">Analytics dashboard coming soon...</p>
+    </div>
+  ),
+});