feat(live): refresh the channel list on demand and on resume

Live categories and channels were fetched once per app session and kept
in memory until the process died, so a TV box left running never picked
up provider changes.

- Live tab: pull-to-refresh plus a remote-friendly refresh button, and an
  automatic refetch when the app returns to the foreground after 4 hours.
- Settings: the "refresh cache" entry was a no-op delay; it now forces a
  reload of live channels, movies, series and EPG.
- The Xtream service keeps the last non-empty live lists and serves them
  when a refetch fails, so a refresh on a not-yet-connected network does
  not blank the screen.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

lib/features/iptv/widgets/mobile_series_tab.dart

@@ -216,6 +216,7 @@ class _MobileSeriesTabState extends ConsumerState<MobileSeriesTab>
   @override
   Widget build(BuildContext context) {
     super.build(context);
+    ref.listen<int>(fullCatalogRefreshTickProvider, (_, __) => _refresh());
     final settings = ref.watch(mobileSettingsProvider);
 
     if (_categories.isEmpty && !_isLoading) {