📱 refactor(web): remove legacy isMobile util and migrate to useIsMobile hook

BREAKING CHANGE:
helpers/utils.js no longer exports `isMobile()`.
Any external code that relied on this function must switch to the `useIsMobile` React hook.

Summary
-------
1. Deleted the obsolete `isMobile()` function from helpers/utils.js.
2. Introduced `MOBILE_BREAKPOINT` constant and `matchMedia`-based detection for non-React contexts.
3. Reworked toast positioning logic in utils.js to rely on `matchMedia`.
4. Updated render.js:
   • Removed isMobile import.
   • Added MOBILE_BREAKPOINT detection in `truncateText`.
5. Migrated every page/component to the `useIsMobile` hook:
   • Layout: HeaderBar, PageLayout, SiderBar
   • Pages: Home, Detail, Playground, User (Add/Edit), Token, Channel, Redemption, Ratio Sync
   • Components: ChannelsTable, ChannelSelectorModal, ConflictConfirmModal
6. Purged all remaining `isMobile()` calls and legacy imports.
7. Added missing `const isMobile = useIsMobile()` declarations where required.

Benefits
--------
• Unifies mobile detection with a React-friendly hook.
• Eliminates duplicated logic and improves maintainability.
• Keeps non-React helpers lightweight by using `matchMedia` directly.

web/src/components/table/ChannelsTable.js

@@ -44,7 +44,8 @@ import {
   IconMore,
   IconDescend2
 } from '@douyinfe/semi-icons';
-import { loadChannelModels, isMobile, copy } from '../../helpers';
+import { loadChannelModels, copy } from '../../helpers';
+import { useIsMobile } from '../../hooks/useIsMobile.js';
 import EditTagModal from '../../pages/Channel/EditTagModal.js';
 import { useTranslation } from 'react-i18next';
 import { useTableCompactMode } from '../../hooks/useTableCompactMode';
@@ -52,6 +53,7 @@ import { FaRandom } from 'react-icons/fa';
 
 const ChannelsTable = () => {
   const { t } = useTranslation();
+  const isMobile = useIsMobile();
 
   let type2label = undefined;
 
@@ -2031,7 +2033,7 @@ const ChannelsTable = () => {
         }
         maskClosable={!isBatchTesting}
         className="!rounded-lg"
-        size={isMobile() ? 'full-width' : 'large'}
+        size={isMobile ? 'full-width' : 'large'}
       >
         <div className="model-test-scroll">
           {currentTestChannel && (