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/package.json

@@ -12,6 +12,8 @@
   "dependencies": {
     "@tailwindcss/forms": "^0.5.10",
     "@tanstack/react-query": "^5.87.1",
+    "@tanstack/react-router": "^1.131.36",
+    "@tanstack/router-cli": "^1.131.36",
     "autoprefixer": "^10.4.21",
     "axios": "^1.11.0",
     "clsx": "^2.1.1",
@@ -23,6 +25,7 @@
   },
   "devDependencies": {
     "@eslint/js": "^9.33.0",
+    "@tanstack/router-vite-plugin": "^1.131.36",
     "@types/react": "^19.1.10",
     "@types/react-dom": "^19.1.7",
     "@vitejs/plugin-react": "^5.0.0",