feat: add Layer 2 - WhatsApp Core logic, API Gateway models/auth, Frontend core

WhatsApp Core:
- SessionManager with Baileys integration for multi-account support
- Express server with REST API and Socket.IO for real-time events
- Session lifecycle management (create, disconnect, delete)
- Message sending with support for text, image, document, audio, video

API Gateway:
- Database models: User, WhatsAppAccount, Contact, Conversation, Message
- JWT authentication with access/refresh tokens
- Auth endpoints: login, refresh, register, me
- Pydantic schemas for request/response validation

Frontend:
- React 18 app structure with routing
- Zustand auth store with persistence
- API client with automatic token handling
- Base CSS and TypeScript declarations

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

frontend/src/App.tsx

@@ -0,0 +1,33 @@
+import { Routes, Route, Navigate } from 'react-router-dom';
+import { useAuthStore } from './store/auth';
+
+// Placeholder components - will be replaced
+const LoginPage = () => <div>Login Page</div>;
+const DashboardPage = () => <div>Dashboard</div>;
+const MainLayout = ({ children }: { children: React.ReactNode }) => <div>{children}</div>;
+
+function PrivateRoute({ children }: { children: React.ReactNode }) {
+  const isAuthenticated = useAuthStore((state) => state.isAuthenticated);
+  return isAuthenticated ? <>{children}</> : <Navigate to="/login" replace />;
+}
+
+export default function App() {
+  return (
+    <Routes>
+      <Route path="/login" element={<LoginPage />} />
+      <Route
+        path="/*"
+        element={
+          <PrivateRoute>
+            <MainLayout>
+              <Routes>
+                <Route path="/" element={<Navigate to="/dashboard" replace />} />
+                <Route path="/dashboard" element={<DashboardPage />} />
+              </Routes>
+            </MainLayout>
+          </PrivateRoute>
+        }
+      />
+    </Routes>
+  );
+}