🎨 refactor(ui): use lucide-react for search/refresh and chevron icons

- DashboardHeader.jsx: replace Semi's IconSearch/IconRefresh with lucide-react's Search/RefreshCw (size 16), preserve existing button styles
- UptimePanel.jsx: replace Semi's IconRefresh with lucide-react's RefreshCw (size 14), keep styling intact
- UserArea.jsx: replace Semi's IconChevronDown with lucide-react's ChevronDown (size 14), preserve visual parity
- Update imports: remove @douyinfe/semi-icons usage where replaced; add lucide-react imports
- Verified no remaining IconSearch/IconRefresh in dashboard; no new linter errors

Motivation: unify icon library for core actions and improve UI consistency.
Follow-ups: consider migrating remaining Semi icons (e.g., plus/minus, charts) to lucide-react.

web/src/components/dashboard/DashboardHeader.jsx

@@ -19,7 +19,7 @@ For commercial licensing, please contact support@quantumnous.com
 
 import React from 'react';
 import { Button } from '@douyinfe/semi-ui';
-import { IconRefresh, IconSearch } from '@douyinfe/semi-icons';
+import { RefreshCw, Search } from 'lucide-react';
 
 const DashboardHeader = ({
   getGreeting,
@@ -42,13 +42,13 @@ const DashboardHeader = ({
       <div className="flex gap-3">
         <Button
           type='tertiary'
-          icon={<IconSearch />}
+          icon={<Search size={16} />}
           onClick={showSearchModal}
           className={`bg-green-500 hover:bg-green-600 ${ICON_BUTTON_CLASS}`}
         />
         <Button
           type='tertiary'
-          icon={<IconRefresh />}
+          icon={<RefreshCw size={16} />}
           onClick={refresh}
           loading={loading}
           className={`bg-blue-500 hover:bg-blue-600 ${ICON_BUTTON_CLASS}`}