feat: add general chat feature (without project/agent concept)

frontend/src/App.tsx

@@ -2,6 +2,7 @@ import { Routes, Route, Navigate } from 'react-router-dom'
 import MainLayout from './layouts/MainLayout'
 import HomePage from './pages/HomePage'
 import AgentChatPage from './pages/AgentChatPage'
+import ChatPage from './pages/ChatPage'
 import KnowledgePage from './pages/KnowledgePage'
 import HistoryPage from './pages/HistoryPage'
 
@@ -10,6 +11,7 @@ function App() {
     <Routes>
       <Route path="/" element={<MainLayout />}>
         <Route index element={<HomePage />} />
+        <Route path="chat" element={<ChatPage />} />
         <Route path="agent/:agentId" element={<AgentChatPage />} />
         <Route path="knowledge" element={<KnowledgePage />} />
         <Route path="history" element={<HistoryPage />} />