feat(studyset): an empty tab says its material is in the topics, and leads there

People testing the app looked for the material of a studyset that groups
topics in its own empty tabs, which said "No flashcards yet" and how to
add some. A tab with none of its own while the topics hold some now says
so: "The flashcards are in its topics", each topic holding some with how
much (everything inside it counted), opening it; for flashcards Browse
all of them in one list; and, quieter, how to add some here after all.
Opened for the first time, such a studyset shows the first tab its topics
fill. The tabs' counts stay the studyset's own.

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

halkyon_learn_flutter/lib/l10n/app_localizations_de.dart

@@ -1041,6 +1041,46 @@ class AppLocalizationsDe extends AppLocalizations {
   @override
   String get studysetAddMaterial => 'Material hinzufügen';
 
+  @override
+  String get studysetPathsInTopics => 'Die Pfade sind in seinen Themen';
+
+  @override
+  String get studysetPathsInTopicsHint =>
+      'Oder schreib hier einen: „Material hinzufügen → Pfad erstellen“.';
+
+  @override
+  String get studysetFlashcardsInTopics =>
+      'Die Karteikarten sind in seinen Themen';
+
+  @override
+  String get studysetFlashcardsInTopicsHint =>
+      'Oder füg hier welche hinzu: „Material hinzufügen → Karteikarten erstellen“.';
+
+  @override
+  String get studysetNotesInTopics => 'Die Notizen sind in seinen Themen';
+
+  @override
+  String get studysetNotesInTopicsHint =>
+      'Oder schreib hier eine: „Material hinzufügen → Notiz erstellen“.';
+
+  @override
+  String get studysetFilesInTopics => 'Die Dateien sind in seinen Themen';
+
+  @override
+  String get studysetFilesInTopicsHint =>
+      'Oder füg hier eine hinzu: „Material hinzufügen → PDF hochladen“.';
+
+  @override
+  String studysetBrowseAllFlashcards(int count) {
+    String _temp0 = intl.Intl.pluralLogic(
+      count,
+      locale: localeName,
+      other: 'Alle $count ansehen',
+      one: 'Ansehen',
+    );
+    return '$_temp0';
+  }
+
   @override
   String get studysetCreateFlashcards => 'Karteikarten erstellen';