perf(tv): evict non-adjacent season episode pages on low-end hardware

Visited seasons' 200-item pages were retained for the screen's
lifetime — irrelevant for a 3-season show, tens of MB of Dart heap for
a 30-season one. Low-end TV now keeps the prefetch window (selected
season plus/minus one); evicted seasons transparently refetch through the
existing unloaded-hub path.

Ref #1349

lib/screens/media_detail_screen.dart

@@ -6,6 +6,7 @@ import 'package:cached_network_image_ce/cached_network_image.dart';
 import 'package:flutter/material.dart';
 
 import '../navigation/profile_navigation_scope.dart';
+import '../services/device_performance.dart';
 import '../services/image_cache_service.dart';
 import 'package:flutter/services.dart';
 import 'package:plezy/utils/platform_detector.dart';
@@ -155,6 +156,14 @@ class _SeasonEpisodePager {
     _moreLoadsInFlight.remove(seasonId);
   }
 
+  /// Drops cached episode pages for seasons outside [keepSeasonIds].
+  /// In-flight sets are left alone — a completing prefetch just re-adds one
+  /// bounded page. Evicted seasons transparently refetch through the normal
+  /// unloaded-hub path when refocused.
+  void retainOnly(Set<String> keepSeasonIds) {
+    _states.removeWhere((seasonId, _) => !keepSeasonIds.contains(seasonId));
+  }
+
   void removeEpisode(String episodeId) {
     for (final entry in _states.entries.toList()) {
       _states[entry.key] = entry.value.removeWhere((episode) => episode.id == episodeId);
@@ -4023,6 +4032,7 @@ class _MediaDetailScreenState extends State<MediaDetailScreen>
         _episodes = List.of(_seasonEpisodePager.stateFor(season.id).items);
       });
       unawaited(_prefetchAdjacentSeasonEpisodePages(seasonIndex));
+      _pruneDistantSeasonPages(seasonIndex);
       return;
     }
 
@@ -4033,6 +4043,20 @@ class _MediaDetailScreenState extends State<MediaDetailScreen>
     });
     unawaited(_fetchSeasonEpisodes(seasonIndex));
     unawaited(_prefetchAdjacentSeasonEpisodePages(seasonIndex));
+    _pruneDistantSeasonPages(seasonIndex);
+  }
+
+  /// Low-end TV only: keep episode pages for the selected season ±1 (the
+  /// prefetch window) and drop the rest. Visited 200-item pages otherwise
+  /// accumulate for the screen's lifetime — irrelevant for a 3-season show,
+  /// tens of MB of retained heap for a 30-season one.
+  void _pruneDistantSeasonPages(int seasonIndex) {
+    if (!DevicePerformance.isLowEndHardware || !PlatformDetector.isTV()) return;
+    final keep = <String>{
+      for (var i = seasonIndex - 1; i <= seasonIndex + 1; i++)
+        if (i >= 0 && i < _seasons.length) _seasons[i].id,
+    };
+    _seasonEpisodePager.retainOnly(keep);
   }
 
   /// What the rail should show in a hub's trailing slot: a spinner while the