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/vite.config.ts

@@ -1,7 +1,11 @@
 import { defineConfig } from "vite";
 import react from "@vitejs/plugin-react";
+import { TanStackRouterVite } from "@tanstack/router-vite-plugin";
 
 // https://vite.dev/config/
 export default defineConfig({
-  plugins: [react()],
+  plugins: [
+    TanStackRouterVite(),
+    react(),
+  ],
 });