feat(study): a kanji's answer shows the studyset's words written with it

A character card's answer lists up to five vocabulary cards of the
studysets the session studies whose front holds the character, with
their reading and first meanings; a tap opens the word's card. The words
come from every card the session reads, whatever tags narrow it, so a
session of kanji alone still shows them, and nothing is fetched: it works
offline.

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

@@ -1748,5 +1748,6 @@
   "suggestIntro": "The author sees it as you have it now, beside theirs. Public: everyone learning it reads it, with your public profile.",
   "suggestSent": "Suggestion sent.",
   "suggestNoDerivatives": "Its licence forbids adaptations: no suggestions.",
-  "feedbackNeedsIdentity": "Sign in with GitHub to report to the author and suggest."
+  "feedbackNeedsIdentity": "Sign in with GitHub to report to the author and suggest.",
+  "kanjiExampleWords": "Words with it"
 }