fix(card): the browser's title says how many cards, sub-studysets on a line below

The card browser's title ran "Japanese — flashcards (incl.
sub-studysets)". The sub-studysets now go on a small line of their own
below the title, and the title has how many cards there are beside it,
in the badge the material's tabs show their counts in (CountBadge, now
shared).

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01MMm7usAo6q9ZZRoPkWjoxi
Signed-off-by: Tizian 「ティツィアーン」 <raisondetredev@pm.me>

halkyon_learn_flutter/lib/l10n/app_localizations_de.dart

@@ -5203,9 +5203,7 @@ class AppLocalizationsDe extends AppLocalizations {
   }
 
   @override
-  String cardBrowserTitleSubtree(String title) {
-    return '$title (mit Unter-Lernsets)';
-  }
+  String get cardBrowserWithSubstudysets => 'Mit seinen Unter-Lernsets';
 
   @override
   String get cardBrowserBrowse => 'Durchsuchen';