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

@@ -0,0 +1,10 @@
+import { Routes, Route } from "react-router-dom";
+import HomePage from "./pages/HomePage";
+
+export default function App() {
+  return (
+    <Routes>
+      <Route path="/" element={<HomePage />} />
+    </Routes>
+  );
+}