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_de.arb

@@ -567,16 +567,19 @@
   "composerKindVocabulary": "Vokabel",
   "composerKindMatching": "Zuordnung",
   "composerKindMap": "Landkarte",
+  "composerKindCharacter": "Schriftzeichen",
   "composerLabelFront": "Vorderseite",
   "composerLabelQuestion": "Frage",
   "composerLabelExpression": "Ausdruck",
   "composerLabelPrompt": "Aufgabe",
+  "composerLabelCharacter": "Schriftzeichen",
   "composerLabelBack": "Rückseite",
   "composerLabelAnswers": "Antworten",
   "composerLabelAnswer": "Antwort",
   "composerPlaceholderFront": "Frage hinzufügen",
   "composerPlaceholderExpression": "Ausdruck hinzufügen",
   "composerPlaceholderPrompt": "Aufgabe hinzufügen",
+  "composerPlaceholderCharacter": "Kanji oder Kana hinzufügen",
   "composerAddAnswer": "Antwort hinzufügen",
   "composerCorrectAnswer": "Richtige Antwort",
   "composerWrongAnswer": "Falsche Antwort",
@@ -623,6 +626,13 @@
   "vocabularyRemoveGloss": "Übersetzung entfernen",
   "vocabularyAddSense": "Wortbedeutung hinzufügen",
   "vocabularyRemoveSense": "Wortbedeutung entfernen",
+  "characterPrimaryMeaningHint": "Hauptbedeutung, bei Kana die Umschrift",
+  "characterOnReadings": "On-Lesungen",
+  "characterOnReadingsHint": "Aus dem Chinesischen, in Katakana: ショク、ジキ",
+  "characterKunReadings": "Kun-Lesungen",
+  "characterKunReadingsHint": "Japanisch, in Hiragana, Okurigana nach einem Punkt: た.べる",
+  "characterOn": "On",
+  "characterKun": "Kun",
   "matchingCategories": "Kategorien",
   "matchingCategoriesHint": "Die Ablagekarten, auf die Lernende Elemente ziehen. Jede Kategorie braucht mindestens ein Element, daher kann eine Karte nicht mehr Kategorien als Elemente haben.",
   "matchingCategory": "Kategorie {number}",
@@ -1213,6 +1223,7 @@
   "cardBrowserTypeVocabulary": "Nur Wörter",
   "cardBrowserTypeMatching": "Nur Zuordnungen",
   "cardBrowserTypeMap": "Nur Karten",
+  "cardBrowserTypeCharacter": "Nur Schriftzeichen",
   "cardBrowserFilterTag": "Tag",
   "cardBrowserAllTags": "Alle Tags",
   "cardBrowserFilterStatus": "Stand",