feat(frontend): implement complete React frontend with Vite, TypeScript, and Tailwind

Complete frontend implementation (FE-001 to FE-006):

FE-001: Setup Ambiente React
- Initialize Vite + React + TypeScript project
- Configure Tailwind CSS with custom theme
- Add shadcn/ui components (Button, Card, Badge, Table, DropdownMenu, Toaster)
- Install dependencies: axios, react-query, react-router-dom, lucide-react, etc.
- Configure path aliases (@/components, @/lib, etc.)

FE-002: Configurazione API Client
- Create lib/api.ts with Axios instance
- Add TypeScript types for Scenario, Metrics, etc.
- Configure environment variable VITE_API_URL

FE-003: React Query Hooks
- Create QueryProvider with React Query client
- Add useScenarios hook with pagination/filters
- Add useScenario hook for detail view
- Add mutations: create, update, delete, start, stop
- Add useMetrics hook with auto-refresh
- Implement cache invalidation

FE-004: Layout e Navigazione
- Create Layout component with Header and Sidebar
- Configure React Router with routes:
  * / - Dashboard
  * /scenarios - Scenarios list
  * /scenarios/:id - Scenario detail
- Implement responsive navigation
- Add active state styling

FE-005: Dashboard Page
- Create Dashboard with stat cards
- Display total scenarios, running count, total cost, PII violations
- Use real data from useScenarios hook
- Add loading states

FE-006: Scenarios List Page
- Create ScenariosPage with data table
- Display scenario name, status (with badge), region, requests, cost
- Add action dropdown (Start, Stop, Delete)
- Implement navigation to detail view

Components Created:
- ui/button.tsx - Button component with variants
- ui/card.tsx - Card component with header/content/footer
- ui/badge.tsx - Badge component for status
- ui/table.tsx - Table component
- ui/dropdown-menu.tsx - Dropdown menu
- ui/toaster.tsx - Toast notifications

Pages Created:
- Dashboard.tsx - Main dashboard view
- ScenariosPage.tsx - List of scenarios
- ScenarioDetail.tsx - Scenario detail with metrics
- NotFound.tsx - 404 page

All features integrated with backend API.

Tasks: FE-001, FE-002, FE-003, FE-004, FE-005, FE-006 complete

frontend/src/App.tsx

@@ -0,0 +1,28 @@
+import { BrowserRouter, Routes, Route } from 'react-router-dom';
+import { QueryProvider } from './providers/QueryProvider';
+import { Toaster } from '@/components/ui/toaster';
+import { Layout } from './components/layout/Layout';
+import { Dashboard } from './pages/Dashboard';
+import { ScenariosPage } from './pages/ScenariosPage';
+import { ScenarioDetail } from './pages/ScenarioDetail';
+import { NotFound } from './pages/NotFound';
+
+function App() {
+  return (
+    <QueryProvider>
+      <BrowserRouter>
+        <Routes>
+          <Route path="/" element={<Layout />}>
+            <Route index element={<Dashboard />} />
+            <Route path="scenarios" element={<ScenariosPage />} />
+            <Route path="scenarios/:id" element={<ScenarioDetail />} />
+            <Route path="*" element={<NotFound />} />
+          </Route>
+        </Routes>
+      </BrowserRouter>
+      <Toaster />
+    </QueryProvider>
+  );
+}
+
+export default App;