feat: add React frontend with auth, project list, import, and project detail pages

Converts packages/web from vanilla TypeScript Vite scaffold to React with:
- React 19, react-router-dom v7, @tanstack/react-query v5, Tailwind CSS v4
- JWT auth context with auto-refresh token support
- Login/Register pages, protected Layout with auth guard
- Projects list with grid cards and delete action
- ImportDialog supporting URL or file upload with API key display
- ProjectDetail with 4 tabs: Documentation, Modules, MCP Integration, Settings
- All TypeScript compiles cleanly (noEmit check passes)

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

packages/web/src/pages/Layout.tsx

@@ -0,0 +1,22 @@
+import { Navigate, Outlet } from 'react-router-dom';
+import { useAuth } from '../lib/auth';
+
+export default function Layout() {
+  const { user, loading, logout } = useAuth();
+
+  if (loading) return <div className="min-h-screen flex items-center justify-center">Loading...</div>;
+  if (!user) return <Navigate to="/login" replace />;
+
+  return (
+    <div className="min-h-screen bg-gray-50">
+      <header className="bg-white border-b px-6 py-3 flex items-center justify-between">
+        <h1 className="text-lg font-semibold">Agent Fox</h1>
+        <div className="flex items-center gap-4">
+          <span className="text-sm text-gray-600">{user.name}</span>
+          <button onClick={logout} className="text-sm text-red-600 hover:underline">Sign Out</button>
+        </div>
+      </header>
+      <main className="p-6"><Outlet /></main>
+    </div>
+  );
+}