feat: Phase 7 - Frontend scaffolding and auth (T-023, T-024, T-025)

T-023: Initialize React project
- Vite + React 19 + TypeScript scaffold
- Tailwind CSS v4 with @tailwindcss/vite plugin
- Dependencies: react-router-dom, axios, @tanstack/react-query, lucide-react
- Project structure: api/, components/, pages/, context/, types/, hooks/, lib/

T-024: API client and auth context
- Axios client with JWT interceptor (auto-attach token, clear on 401)
- login() and getMe() API functions
- AuthContext: user state, login, logout, isAuthenticated, isLoading
- Token persistence via localStorage with hydration on mount
- TypeScript types for all backend models

T-025: Login page and layout
- LoginPage with form, error handling, redirect on success
- Layout with sidebar + header + Outlet
- Sidebar with role-aware navigation (System only for admin)
- ProtectedRoute wrapper with role-based access control
- Routes: /login, /dashboard, /techniques, /tests, /system

frontend/src/pages/DashboardPage.tsx

@@ -0,0 +1,15 @@
+import { Shield } from "lucide-react";
+
+export default function DashboardPage() {
+  return (
+    <div className="space-y-4">
+      <h1 className="text-2xl font-bold text-white">Dashboard</h1>
+      <div className="flex items-center gap-3 rounded-xl border border-gray-800 bg-gray-900 p-6">
+        <Shield className="h-8 w-8 text-cyan-400" />
+        <p className="text-gray-300">
+          Coverage metrics will appear here.
+        </p>
+      </div>
+    </div>
+  );
+}