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_localizations_en.dart

@@ -1732,6 +1732,114 @@ class AppLocalizationsEn extends AppLocalizations {
   @override
   String get cardSenses => 'Senses';
 
+  @override
+  String get cardDictionaryEntry => 'Dictionary entry';
+
+  @override
+  String get studysetFromDictionary => 'From the dictionary';
+
+  @override
+  String get dictionaryTitle => 'Dictionary';
+
+  @override
+  String get dictionarySearchHint =>
+      'A word in kanji, kana or romaji, or a meaning';
+
+  @override
+  String dictionaryNothingFound(String query) {
+    return 'Nothing found for “$query”.';
+  }
+
+  @override
+  String get dictionaryUnreachable =>
+      'The dictionary can\'t be reached right now.';
+
+  @override
+  String get dictionaryRetry => 'Retry';
+
+  @override
+  String get dictionaryAdd => 'Add';
+
+  @override
+  String get dictionaryInStudyset => 'In this studyset';
+
+  @override
+  String dictionaryAdded(String word) {
+    return 'Added “$word”.';
+  }
+
+  @override
+  String get dictionaryLevels => 'Add a whole level';
+
+  @override
+  String get dictionaryLevelsHint =>
+      'Every word of a level becomes a flashcard, in the order of the level\'s list, tagged with its level and word class. Words already in this studyset are left out.';
+
+  @override
+  String get dictionaryLabelCommon => 'Common';
+
+  @override
+  String dictionaryAddLevel(int count) {
+    String _temp0 = intl.Intl.pluralLogic(
+      count,
+      locale: localeName,
+      other: 'Add $count words',
+      one: 'Add 1 word',
+    );
+    return '$_temp0';
+  }
+
+  @override
+  String dictionaryAddingLevel(int done, int count) {
+    return 'Adding… $done of $count';
+  }
+
+  @override
+  String dictionaryWordsAdded(int count) {
+    String _temp0 = intl.Intl.pluralLogic(
+      count,
+      locale: localeName,
+      other: 'Added $count words.',
+      one: 'Added 1 word.',
+      zero: 'No new words.',
+    );
+    return '$_temp0';
+  }
+
+  @override
+  String dictionaryWordsSkipped(int count) {
+    String _temp0 = intl.Intl.pluralLogic(
+      count,
+      locale: localeName,
+      other: '$count were in this studyset already.',
+      one: '1 was in this studyset already.',
+    );
+    return '$_temp0';
+  }
+
+  @override
+  String dictionaryConfirmTitle(int count) {
+    return 'Add $count words?';
+  }
+
+  @override
+  String get dictionaryConfirmMessage =>
+      'Each becomes a flashcard in this studyset.';
+
+  @override
+  String get dictionaryConfirmAdd => 'Add';
+
+  @override
+  String dictionaryCredits(String sources) {
+    return 'Words from $sources.';
+  }
+
+  @override
+  String get dictionaryLookUp => 'Look up in the dictionary';
+
+  @override
+  String get aboutDictionaries => 'Dictionaries on this instance';
+
   @override
   String get cardReportTitle => 'Report an error';