Add full-stack BTC portfolio web app

Multi-user FastAPI + React app with JWT auth, SQLite storage, and
CoinGecko price integration. Dockerized with docker-compose.

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

btc-portfolio/frontend/src/App.js

@@ -0,0 +1,22 @@
+import React from 'react';
+import { BrowserRouter, Routes, Route, Navigate } from 'react-router-dom';
+import Login from './pages/Login';
+import Register from './pages/Register';
+import Dashboard from './pages/Dashboard';
+
+function PrivateRoute({ children }) {
+  return localStorage.getItem('token') ? children : <Navigate to="/login" />;
+}
+
+export default function App() {
+  return (
+    <BrowserRouter>
+      <Routes>
+        <Route path="/login" element={<Login />} />
+        <Route path="/register" element={<Register />} />
+        <Route path="/" element={<PrivateRoute><Dashboard /></PrivateRoute>} />
+        <Route path="*" element={<Navigate to="/" />} />
+      </Routes>
+    </BrowserRouter>
+  );
+}