📱 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/helpers/render.js

@@ -1,6 +1,7 @@
 import i18next from 'i18next';
 import { Modal, Tag, Typography } from '@douyinfe/semi-ui';
-import { copy, isMobile, showSuccess } from './utils';
+import { copy, showSuccess } from './utils';
+import { MOBILE_BREAKPOINT } from '../hooks/useIsMobile.js';
 import { visit } from 'unist-util-visit';
 import {
   OpenAI,
@@ -669,7 +670,8 @@ const measureTextWidth = (
 };
 
 export function truncateText(text, maxWidth = 200) {
-  if (!isMobile()) {
+  const isMobileScreen = window.matchMedia(`(max-width: ${MOBILE_BREAKPOINT - 1}px)`).matches;
+  if (!isMobileScreen) {
     return text;
   }
   if (!text) return text;