📱 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/pages/Token/EditToken.js

@@ -1,7 +1,6 @@
 import React, { useEffect, useState, useContext, useRef } from 'react';
 import {
   API,
-  isMobile,
   showError,
   showSuccess,
   timestamp2string,
@@ -9,6 +8,7 @@ import {
   renderQuotaWithPrompt,
   getModelCategories,
 } from '../../helpers';
+import { useIsMobile } from '../../hooks/useIsMobile.js';
 import {
   Button,
   SideSheet,
@@ -38,6 +38,7 @@ const EditToken = (props) => {
   const { t } = useTranslation();
   const [statusState, statusDispatch] = useContext(StatusContext);
   const [loading, setLoading] = useState(false);
+  const isMobile = useIsMobile();
   const formApiRef = useRef(null);
   const [models, setModels] = useState([]);
   const [groups, setGroups] = useState([]);
@@ -277,7 +278,7 @@ const EditToken = (props) => {
       }
       bodyStyle={{ padding: '0' }}
       visible={props.visiable}
-      width={isMobile() ? '100%' : 600}
+      width={isMobile ? '100%' : 600}
       footer={
         <div className='flex justify-end bg-white'>
           <Space>