fix: eliminate duplicate API requests on startup

- Skip redundant notifyListeners in HiddenLibrariesProvider init when
  set is empty (empty→empty is a no-op for consumers)
- Track last-seen hidden keys in DiscoverScreen to avoid reloading
  content when the listener fires without an actual change
- Track previous online server set in MultiServerProvider; only re-check
  DVR availability when a new server comes online
- Remove dead content-loading pipeline from libraries_screen (sorts,
  pagination, filters, items) that was never rendered
- Move /media/providers fetch into PlexClient.create() init, replacing
  lazy EPG cache and providing libraries including shared items

lib/screens/livetv/live_tv_screen.dart

@@ -130,21 +130,14 @@ class _LiveTvScreenState extends State<LiveTvScreen>
         'Live TV DVRs: ${liveTvServers.map((s) => '${s.serverId}/${s.dvrKey} lineup=${s.lineup}').join(', ')}',
       );
 
-      // Build a set of enabled channel keys per server from DVR mappings
+      // Build a set of enabled channel keys per server from cached DVR data
       final enabledKeysByServer = <String, Set<String>>{};
-      final queriedServers = <String>{};
+      final processedServers = <String>{};
       for (final serverInfo in liveTvServers) {
-        if (!queriedServers.add(serverInfo.serverId)) continue;
-        try {
-          final client = multiServer.getClientForServer(serverInfo.serverId);
-          if (client == null) continue;
-          final dvrs = await client.getDvrs();
-          final enabledKeys = _extractEnabledChannelKeys(dvrs);
-          if (enabledKeys != null) {
-            enabledKeysByServer[serverInfo.serverId] = enabledKeys;
-          }
-        } catch (e) {
-          appLogger.e('Failed to load DVR mappings for server ${serverInfo.serverId}', error: e);
+        if (!processedServers.add(serverInfo.serverId)) continue;
+        final enabledKeys = _extractEnabledChannelKeys(serverInfo.dvrs);
+        if (enabledKeys != null) {
+          enabledKeysByServer[serverInfo.serverId] = enabledKeys;
         }
       }