📱 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/index.js

@@ -6,7 +6,6 @@ import { UserProvider } from './context/User';
 import 'react-toastify/dist/ReactToastify.css';
 import { StatusProvider } from './context/Status';
 import { ThemeProvider } from './context/Theme';
-import { StyleProvider } from './context/Style/index.js';
 import PageLayout from './components/layout/PageLayout.js';
 import './i18n/i18n.js';
 import './index.css';
@@ -20,9 +19,7 @@ root.render(
       <UserProvider>
         <BrowserRouter>
           <ThemeProvider>
-            <StyleProvider>
-              <PageLayout />
-            </StyleProvider>
+            <PageLayout />
           </ThemeProvider>
         </BrowserRouter>
       </UserProvider>