fix(buscar): rebuild the offline banner with offlineAccent

Audit 13.1 (t4 line 641): the banner rendered wifi_off in
colorScheme.error (red) inside a generic glass card. Rebuilt using
offlineAccent (#E8879A) — a token that existed since Tier 1 with no
consumer — for the tint, border and icon, plus the prototype's title/
detail layout and a restyled Retry chip. New offlineBannerTitle key
translated to all 13 locales.

lib/l10n/gen/app_localizations_zh.dart

@@ -737,6 +737,9 @@ class AppLocalizationsZh extends AppLocalizations {
   @override
   String get genresTitle => '类型';
 
+  @override
+  String get offlineBannerTitle => '无连接';
+
   @override
   String get retryAction => '重试';