chore: initial project setup

Phase 0 — full project scaffold with:
- Backend: FastAPI + SQLAlchemy 2.0 async + Alembic + PostgreSQL 16
- Frontend: React 18 + TypeScript + Vite + Tailwind CSS + shadcn/ui
- Docker Compose (prod + dev override with hot-reload)
- Health endpoint, CORS config, API proxy, env template

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

frontend/src/App.tsx

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+import { Routes, Route } from "react-router-dom";
+import HomePage from "./pages/HomePage";
+
+export default function App() {
+  return (
+    <Routes>
+      <Route path="/" element={<HomePage />} />
+    </Routes>
+  );
+}

frontend/src/api/client.ts

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+import axios from "axios";
+
+export const apiClient = axios.create({
+  baseURL: "/api",
+  headers: {
+    "Content-Type": "application/json",
+  },
+});

frontend/src/index.css

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+@tailwind base;
+@tailwind components;
+@tailwind utilities;
+
+@layer base {
+  :root {
+    --background: 0 0% 100%;
+    --foreground: 222.2 84% 4.9%;
+    --card: 0 0% 100%;
+    --card-foreground: 222.2 84% 4.9%;
+    --popover: 0 0% 100%;
+    --popover-foreground: 222.2 84% 4.9%;
+    --primary: 221.2 83.2% 53.3%;
+    --primary-foreground: 210 40% 98%;
+    --secondary: 210 40% 96.1%;
+    --secondary-foreground: 222.2 47.4% 11.2%;
+    --muted: 210 40% 96.1%;
+    --muted-foreground: 215.4 16.3% 46.9%;
+    --accent: 210 40% 96.1%;
+    --accent-foreground: 222.2 47.4% 11.2%;
+    --destructive: 0 84.2% 60.2%;
+    --destructive-foreground: 210 40% 98%;
+    --border: 214.3 31.8% 91.4%;
+    --input: 214.3 31.8% 91.4%;
+    --ring: 221.2 83.2% 53.3%;
+    --radius: 0.5rem;
+  }
+
+  * {
+    @apply border-border;
+  }
+
+  body {
+    @apply bg-background text-foreground;
+    font-feature-settings: "rlig" 1, "calt" 1;
+  }
+}

frontend/src/main.tsx

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+import React from "react";
+import ReactDOM from "react-dom/client";
+import { QueryClient, QueryClientProvider } from "@tanstack/react-query";
+import { BrowserRouter } from "react-router-dom";
+import App from "./App";
+import "./index.css";
+
+const queryClient = new QueryClient({
+  defaultOptions: {
+    queries: {
+      staleTime: 5 * 60 * 1000,
+      retry: 1,
+    },
+  },
+});
+
+ReactDOM.createRoot(document.getElementById("root")!).render(
+  <React.StrictMode>
+    <QueryClientProvider client={queryClient}>
+      <BrowserRouter>
+        <App />
+      </BrowserRouter>
+    </QueryClientProvider>
+  </React.StrictMode>,
+);

frontend/src/pages/HomePage.tsx

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+import { useQuery } from "@tanstack/react-query";
+import { apiClient } from "../api/client";
+
+export default function HomePage() {
+  const { data: health } = useQuery({
+    queryKey: ["health"],
+    queryFn: () => apiClient.get("/health").then((r) => r.data),
+  });
+
+  return (
+    <div className="flex min-h-screen flex-col items-center justify-center bg-background text-foreground">
+      <div className="text-center">
+        <h1 className="text-4xl font-bold tracking-tight">Budget Tracker</h1>
+        <p className="mt-4 text-lg text-muted-foreground">
+          Gérez votre budget personnel en toute simplicité.
+        </p>
+        {health && (
+          <p className="mt-2 text-sm text-muted-foreground">
+            API: {health.status}
+          </p>
+        )}
+      </div>
+    </div>
+  );
+}

frontend/src/vite-env.d.ts

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+/// <reference types="vite/client" />