feat(app): a character card for kanji and kana

One card type for both (card schema 7): the character on the front, its
meanings and a kanji's on and kun readings, each merging on its own. A
kana's romaji is its meaning, so kana are studied, and later written,
exactly as kanji are. The composer offers it beside the other kinds, each
kind of reading on one line (ショク、ジキ); studying shows the character
large and, with the answer, its meanings and readings (the other way round
when asked from the back); the card browser filters by it and finds a kun
reading without its okurigana dot; the Markdown export writes its meanings
and readings.

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

@@ -2029,6 +2029,9 @@ class AppLocalizationsDe extends AppLocalizations {
   @override
   String get composerKindMap => 'Landkarte';
 
+  @override
+  String get composerKindCharacter => 'Schriftzeichen';
+
   @override
   String get composerLabelFront => 'Vorderseite';
 
@@ -2041,6 +2044,9 @@ class AppLocalizationsDe extends AppLocalizations {
   @override
   String get composerLabelPrompt => 'Aufgabe';
 
+  @override
+  String get composerLabelCharacter => 'Schriftzeichen';
+
   @override
   String get composerLabelBack => 'Rückseite';
 
@@ -2059,6 +2065,9 @@ class AppLocalizationsDe extends AppLocalizations {
   @override
   String get composerPlaceholderPrompt => 'Aufgabe hinzufügen';
 
+  @override
+  String get composerPlaceholderCharacter => 'Kanji oder Kana hinzufügen';
+
   @override
   String get composerAddAnswer => 'Antwort hinzufügen';
 
@@ -2221,6 +2230,30 @@ class AppLocalizationsDe extends AppLocalizations {
   @override
   String get vocabularyRemoveSense => 'Wortbedeutung entfernen';
 
+  @override
+  String get characterPrimaryMeaningHint =>
+      'Hauptbedeutung, bei Kana die Umschrift';
+
+  @override
+  String get characterOnReadings => 'On-Lesungen';
+
+  @override
+  String get characterOnReadingsHint =>
+      'Aus dem Chinesischen, in Katakana: ショク、ジキ';
+
+  @override
+  String get characterKunReadings => 'Kun-Lesungen';
+
+  @override
+  String get characterKunReadingsHint =>
+      'Japanisch, in Hiragana, Okurigana nach einem Punkt: た.べる';
+
+  @override
+  String get characterOn => 'On';
+
+  @override
+  String get characterKun => 'Kun';
+
   @override
   String get matchingCategories => 'Kategorien';
 
@@ -4430,6 +4463,9 @@ class AppLocalizationsDe extends AppLocalizations {
   @override
   String get cardBrowserTypeMap => 'Nur Karten';
 
+  @override
+  String get cardBrowserTypeCharacter => 'Nur Schriftzeichen';
+
   @override
   String get cardBrowserFilterTag => 'Tag';