feat(app): scaffold entry point — providers et router minimal

src/app/main.tsx

@@ -0,0 +1,15 @@
+import { StrictMode } from 'react'
+import { createRoot } from 'react-dom/client'
+import { Providers } from './providers'
+import '../index.css'
+
+const container = document.getElementById('root')
+if (!container) {
+  throw new Error('Root element #root introuvable dans index.html')
+}
+
+createRoot(container).render(
+  <StrictMode>
+    <Providers />
+  </StrictMode>,
+)

src/app/providers.tsx

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+import { QueryClient, QueryClientProvider } from '@tanstack/react-query'
+import { BrowserRouter } from 'react-router-dom'
+import { AppRouter } from './router'
+
+const queryClient = new QueryClient({
+  defaultOptions: {
+    queries: {
+      staleTime: 5 * 60 * 1000,
+      retry: false,
+    },
+  },
+})
+
+export function Providers() {
+  return (
+    <QueryClientProvider client={queryClient}>
+      <BrowserRouter>
+        <AppRouter />
+      </BrowserRouter>
+    </QueryClientProvider>
+  )
+}

src/app/router.tsx

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+import { Routes, Route } from 'react-router-dom'
+
+export function AppRouter() {
+  return (
+    <Routes>
+      <Route path="/" element={<ScaffoldPlaceholder />} />
+    </Routes>
+  )
+}
+
+function ScaffoldPlaceholder() {
+  return (
+    <main className="p-6">
+      <h1 className="text-2xl font-semibold">Expria — scaffold Sprint 0</h1>
+      <p>
+        Aucune feature n'est encore branchée. Les routes seront ajoutées au fil
+        des sprints.
+      </p>
+    </main>
+  )
+}