perf(frontend): replace blank Suspense fallbacks with Spin, switch to matchMedia hook, add virtual table scrolling (#6187)

- routes.tsx, LazyMount.tsx: replace Suspense fallback={null} with Spin
  loader so page transitions and lazy modals never show blank content
- useMediaQuery.ts: switch from resize event to matchMedia change event,
  eliminating state updates on every pixel drag; export MOBILE_BREAKPOINT_PX
- SubPage.tsx: drop duplicate inline isMobile logic (7 lines), use shared
  useMediaQuery(576) (2 lines)
- ClientsPage, InboundList, HostList, NodeList: add virtual + scroll.y to
  Table for viewport-only DOM rendering of large datasets

frontend/src/pages/clients/ClientsPage.tsx

@@ -1350,7 +1350,8 @@ export default function ClientsPage() {
                           rowSelection={rowSelection}
                           pagination={tablePagination}
                           size="small"
-                          scroll={{ x: 1200 }}
+                          scroll={{ x: 1200, y: 'calc(100vh - 380px)' }}
+                          virtual
                           onChange={onTableChange}
                           locale={{
                             emptyText: (

frontend/src/pages/hosts/HostList.tsx

@@ -231,7 +231,8 @@ export default function HostList(props: HostListProps) {
         columns={columns}
         dataSource={sorted}
         pagination={false}
-        scroll={{ x: 'max-content' }}
+        scroll={{ x: 'max-content', y: 'calc(100vh - 280px)' }}
+        virtual
         rowSelection={{
           selectedRowKeys: selectedGroupIds,
           onChange: (keys) => onSelectionChange(keys as string[]),

frontend/src/pages/inbounds/list/InboundList.tsx

@@ -286,7 +286,8 @@ export default function InboundList({
               onChange: (keys: Key[]) => setSelectedRowKeys(keys as number[]),
             }}
             pagination={paginationFor(visibleInbounds)}
-            scroll={{ x: tableScrollX }}
+            scroll={{ x: tableScrollX, y: 'calc(100vh - 320px)' }}
+            virtual
             style={{ marginTop: 10 }}
             size="small"
             locale={{

frontend/src/pages/nodes/NodeList.tsx

@@ -648,7 +648,8 @@ export default function NodeList({
           columns={columns}
           pagination={false}
           loading={loading}
-          scroll={{ x: 'max-content' }}
+          scroll={{ x: 'max-content', y: 'calc(100vh - 320px)' }}
+          virtual
           size="middle"
           rowKey="key"
           rowSelection={dataSource.length > 1 ? {

frontend/src/pages/sub/SubPage.tsx

@@ -38,6 +38,7 @@ import { LinkTags, parseLinkParts } from '@/lib/xray/link-label';
 import ConfigBlock from '@/components/clients/ConfigBlock';
 import { setMessageInstance } from '@/utils/messageBus';
 import { pauseAnimationsUntilLeave, useTheme } from '@/hooks/useTheme';
+import { useMediaQuery } from '@/hooks/useMediaQuery';
 import SubUsageSummary from './SubUsageSummary';
 import './SubPage.css';
 
@@ -84,16 +85,9 @@ export default function SubPage() {
   const { isDark, isUltra, toggleTheme, toggleUltra, antdThemeConfig } = useTheme();
   const [messageApi, messageContextHolder] = message.useMessage();
   useEffect(() => { setMessageInstance(messageApi); }, [messageApi]);
-
-  const [isMobile, setIsMobile] = useState<boolean>(() => window.innerWidth < 576);
+  const { isMobile } = useMediaQuery(576);
   const [lang, setLang] = useState<string>(() => LanguageManager.getLanguage());
 
-  useEffect(() => {
-    const onResize = () => setIsMobile(window.innerWidth < 576);
-    window.addEventListener('resize', onResize);
-    return () => window.removeEventListener('resize', onResize);
-  }, []);
-
   const onLangChange = useCallback((next: string) => {
     setLang(next);
     LanguageManager.setLanguage(next);