feat(app): tags keep their case; dictionary tags read JLPT-N5, Noun

A tag is still its name, but no longer in lowercase: the name keeps the
case it was written in, and names that differ only in case are one tag
(ADR 0004, rule 2, amended). Two such tags from two devices fold into the
one with the smaller id, its case with it. Tags stored before stay
lowercase until renamed.

Words from the dictionary are tagged JLPT-N5 to JLPT-N1 and with their
word class (Noun, Verb, i-Adjective, na-Adjective, ...). Anki tags and
PDF chapter tags arrive as written.

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

@@ -1566,7 +1566,8 @@ class AppLocalizationsEn extends AppLocalizations {
   String get tagSheetNameLabel => 'Name';
 
   @override
-  String get tagSheetNameHelper => 'Stored and displayed in lowercase.';
+  String get tagSheetNameHelper =>
+      'Capitals don\'t make another tag: \'Noun\' and \'noun\' are one.';
 
   @override
   String tagSheetNameExists(String name) {