feat(admin): Add activity logs page and fix AI chat markdown rendering

- Add paginated activity logs API with filters (date, module, action, keyword)

- Add ActivityLogsPage with table, filters, and detail modal

- Add markdown rendering support for AI chat messages

- Remove prototype placeholder content from chat sidebar

Co-authored-by: Cursor <cursoragent@cursor.com>

frontend-v2/src/App.tsx

@@ -24,6 +24,8 @@ import UserDetailPage from './modules/admin/pages/UserDetailPage'
 // 系统知识库管理
 import SystemKbListPage from './modules/admin/pages/SystemKbListPage'
 import SystemKbDetailPage from './modules/admin/pages/SystemKbDetailPage'
+// 运营日志
+import ActivityLogsPage from './pages/admin/ActivityLogsPage'
 // 个人中心页面
 import ProfilePage from './pages/user/ProfilePage'
 
@@ -115,6 +117,8 @@ function App() {
                   {/* 系统知识库 */}
                   <Route path="system-kb" element={<SystemKbListPage />} />
                   <Route path="system-kb/:id" element={<SystemKbDetailPage />} />
+                  {/* 运营日志 */}
+                  <Route path="activity-logs" element={<ActivityLogsPage />} />
                   {/* 系统配置 */}
                   <Route path="system" element={<div className="text-center py-20">🚧 系统配置页面开发中...</div>} />
                 </Route>