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/store/blocking.ts

@@ -7,9 +7,22 @@ interface MaintenanceInfo {
   reason?: string;
 }
 
+/**
+ * User-facing channel subscription status returned by the blocking 403 response.
+ * Intentionally separate from `RequiredChannel` (api/adminChannels.ts) which
+ * represents the admin CRUD entity with `is_active` / `sort_order` fields.
+ */
+interface ChannelInfo {
+  channel_id: string;
+  channel_link?: string;
+  title?: string;
+  is_subscribed: boolean;
+}
+
 interface ChannelSubscriptionInfo {
   message: string;
   channel_link?: string;
+  channels?: ChannelInfo[];
 }
 
 interface BlacklistedInfo {