feat(app): the dictionary in the app: look words up, add them as cards

A studyset's dictionary follows from its language, as decided: the
instance's dictionary of its front's language, with meanings in its
back's (else English). Nothing to attach or detach; nothing of it shows
where there is none.

- Add material › From the dictionary: search a word (kanji, kana,
  romaji, meaning) and add it as a flashcard, or add a whole level
  (JLPT N5…N1, common words) at once, asked first above 500 words, its
  progress shown. Words already in the studyset show as such and are
  left out. Each card is a vocabulary card (headword, reading, senses
  with their codes), tagged `jlpt-n5` and with its word class, and
  marked as imported from the dictionary.
- Look up beside a vocabulary card's front fills the card with the word
  chosen, keeping its hints, explanation and tags.
- A card keeps the dictionary entry it was made from (card schema 6:
  `dictionary` {source, id}), to be found again and not added twice.
- The dictionary's credits show at its foot and in About, as its licence
  asks.

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

@@ -487,6 +487,29 @@
   "cardNextHint": "Nächster Hinweis",
   "cardReport": "Meldung",
   "cardSenses": "Wortbedeutungen",
+  "cardDictionaryEntry": "Wörterbucheintrag",
+  "studysetFromDictionary": "Aus dem Wörterbuch",
+  "dictionaryTitle": "Wörterbuch",
+  "dictionarySearchHint": "Ein Wort in Kanji, Kana oder Romaji, oder eine Bedeutung",
+  "dictionaryNothingFound": "Nichts gefunden für „{query}“.",
+  "dictionaryUnreachable": "Das Wörterbuch ist gerade nicht erreichbar.",
+  "dictionaryRetry": "Erneut versuchen",
+  "dictionaryAdd": "Hinzufügen",
+  "dictionaryInStudyset": "In diesem Lernset",
+  "dictionaryAdded": "„{word}“ hinzugefügt.",
+  "dictionaryLevels": "Eine ganze Stufe hinzufügen",
+  "dictionaryLevelsHint": "Jedes Wort einer Stufe wird eine Karteikarte, in der Reihenfolge ihrer Liste, mit Stufe und Wortart als Tags. Wörter, die schon in diesem Lernset sind, werden ausgelassen.",
+  "dictionaryLabelCommon": "Häufig",
+  "dictionaryAddLevel": "{count, plural, =1{1 Wort hinzufügen} other{{count} Wörter hinzufügen}}",
+  "dictionaryAddingLevel": "Wird hinzugefügt… {done} von {count}",
+  "dictionaryWordsAdded": "{count, plural, =0{Keine neuen Wörter.} =1{1 Wort hinzugefügt.} other{{count} Wörter hinzugefügt.}}",
+  "dictionaryWordsSkipped": "{count, plural, =1{1 war schon in diesem Lernset.} other{{count} waren schon in diesem Lernset.}}",
+  "dictionaryConfirmTitle": "{count} Wörter hinzufügen?",
+  "dictionaryConfirmMessage": "Jedes wird eine Karteikarte in diesem Lernset.",
+  "dictionaryConfirmAdd": "Hinzufügen",
+  "dictionaryCredits": "Wörter aus {sources}.",
+  "dictionaryLookUp": "Im Wörterbuch nachschlagen",
+  "aboutDictionaries": "Wörterbücher dieser Instanz",
   "cardReportTitle": "Fehler melden",
   "cardReportSubtitle": "Markiere diese Karte, um sie später zu finden und zu korrigieren.",
   "cardReportTypo": "Tippfehler",