feat: add multi-channel subscription blocking UI and admin management

- Channel subscription blocking screen with per-channel status display
- Safe URL handling with protocol validation (no open redirect)
- Race-condition-safe subscription check with useRef guard
- Admin channel management page with create, toggle, delete
- Error handlers on all admin mutations with haptic feedback
- Proper type guard for channel subscription error detection
- Accessibility: aria-labels on icon-only buttons
- Localization: en, ru, zh, fa translations

src/App.tsx

@@ -87,6 +87,7 @@ const AdminUserDetail = lazy(() => import('./pages/AdminUserDetail'));
 const AdminBroadcastDetail = lazy(() => import('./pages/AdminBroadcastDetail'));
 const AdminPinnedMessages = lazy(() => import('./pages/AdminPinnedMessages'));
 const AdminPinnedMessageCreate = lazy(() => import('./pages/AdminPinnedMessageCreate'));
+const AdminChannelSubscriptions = lazy(() => import('./pages/AdminChannelSubscriptions'));
 const AdminEmailTemplatePreview = lazy(() => import('./pages/AdminEmailTemplatePreview'));
 
 function ProtectedRoute({ children }: { children: React.ReactNode }) {
@@ -854,6 +855,16 @@ function App() {
             </AdminRoute>
           }
         />
+        <Route
+          path="/admin/channel-subscriptions"
+          element={
+            <AdminRoute>
+              <LazyPage>
+                <AdminChannelSubscriptions />
+              </LazyPage>
+            </AdminRoute>
+          }
+        />
         <Route
           path="/admin/email-templates/preview/:type/:lang"
           element={