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/transactions.tsx

@@ -0,0 +1,11 @@
+import { createFileRoute } from "@tanstack/react-router";
+import TransactionsList from "../components/TransactionsList";
+
+export const Route = createFileRoute("/transactions")({
+  component: TransactionsList,
+  validateSearch: (search) => ({
+    accountId: search.accountId as string | undefined,
+    startDate: search.startDate as string | undefined,
+    endDate: search.endDate as string | undefined,
+  }),
+});