📱 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/Detail/index.js

@@ -41,8 +41,9 @@ import { VChart } from '@visactor/react-vchart';
 import {
   API,
   isAdmin,
-  isMobile,
   showError,
+  showSuccess,
+  showWarning,
   timestamp2string,
   timestamp2string1,
   getQuotaWithUnit,
@@ -51,9 +52,9 @@ import {
   renderQuota,
   modelToColor,
   copy,
-  showSuccess,
   getRelativeTime
 } from '../../helpers';
+import { useIsMobile } from '../../hooks/useIsMobile.js';
 import { UserContext } from '../../context/User/index.js';
 import { StatusContext } from '../../context/Status/index.js';
 import { useTranslation } from 'react-i18next';
@@ -66,6 +67,7 @@ const Detail = (props) => {
   // ========== Hooks - Navigation & Translation ==========
   const { t } = useTranslation();
   const navigate = useNavigate();
+  const isMobile = useIsMobile();
 
   // ========== Hooks - Refs ==========
   const formRef = useRef();
@@ -1150,7 +1152,7 @@ const Detail = (props) => {
         onOk={handleSearchConfirm}
         onCancel={handleCloseModal}
         closeOnEsc={true}
-        size={isMobile() ? 'full-width' : 'small'}
+        size={isMobile ? 'full-width' : 'small'}
         centered
       >
         <Form ref={formRef} layout='vertical' className="w-full">