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_en.arb

@@ -535,6 +535,37 @@
   "cardNextHint": "Next hint",
   "cardReport": "Report",
   "cardSenses": "Senses",
+  "cardDictionaryEntry": "Dictionary entry",
+  "studysetFromDictionary": "From the dictionary",
+  "dictionaryTitle": "Dictionary",
+  "dictionarySearchHint": "A word in kanji, kana or romaji, or a meaning",
+  "dictionaryNothingFound": "Nothing found for “{query}”.",
+  "@dictionaryNothingFound": {"placeholders": {"query": {"type": "String"}}},
+  "dictionaryUnreachable": "The dictionary can't be reached right now.",
+  "dictionaryRetry": "Retry",
+  "dictionaryAdd": "Add",
+  "dictionaryInStudyset": "In this studyset",
+  "dictionaryAdded": "Added “{word}”.",
+  "@dictionaryAdded": {"placeholders": {"word": {"type": "String"}}},
+  "dictionaryLevels": "Add a whole level",
+  "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.",
+  "dictionaryLabelCommon": "Common",
+  "dictionaryAddLevel": "{count, plural, =1{Add 1 word} other{Add {count} words}}",
+  "@dictionaryAddLevel": {"placeholders": {"count": {"type": "int"}}},
+  "dictionaryAddingLevel": "Adding… {done} of {count}",
+  "@dictionaryAddingLevel": {"placeholders": {"done": {"type": "int"}, "count": {"type": "int"}}},
+  "dictionaryWordsAdded": "{count, plural, =0{No new words.} =1{Added 1 word.} other{Added {count} words.}}",
+  "@dictionaryWordsAdded": {"placeholders": {"count": {"type": "int"}}},
+  "dictionaryWordsSkipped": "{count, plural, =1{1 was in this studyset already.} other{{count} were in this studyset already.}}",
+  "@dictionaryWordsSkipped": {"placeholders": {"count": {"type": "int"}}},
+  "dictionaryConfirmTitle": "Add {count} words?",
+  "@dictionaryConfirmTitle": {"placeholders": {"count": {"type": "int"}}},
+  "dictionaryConfirmMessage": "Each becomes a flashcard in this studyset.",
+  "dictionaryConfirmAdd": "Add",
+  "dictionaryCredits": "Words from {sources}.",
+  "@dictionaryCredits": {"placeholders": {"sources": {"type": "String"}}},
+  "dictionaryLookUp": "Look up in the dictionary",
+  "aboutDictionaries": "Dictionaries on this instance",
   "cardReportTitle": "Report an error",
   "cardReportSubtitle": "Flag this card so you can find and fix it later.",
   "cardReportTypo": "Typo",