feat(app): stroke order for kanji and kana, from KanjiVG

KanjiVG's strokes come with the app (assets/kanjivg/, CC BY-SA 3.0, its
notice in the licence list): 94 gzipped files, one per 256 code points,
2.7 MB in all, a file read the first time a character of it is asked for
(StrokeRepository, app-wide beside the maps). The strokes are SVG path
data, read with path_parsing (the Flutter team's, pure Dart, already in
the build through flutter_svg), so the model can flatten them into points
without dart:ui, as checking handwriting will.

A character's sheet traces its strokes in order over those to come, with
its stroke count, meanings, readings, level and the components KanjiVG
splits it into, each a tap away. It opens from a studied character's
answer (Stroke order) and from a character found in the dictionary.

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

@@ -1938,6 +1938,18 @@ class AppLocalizationsEn extends AppLocalizations {
     return 'Characters from $sources.';
   }
 
+  @override
+  String get kanjiStrokeOrder => 'Stroke order';
+
+  @override
+  String get kanjiPlayAgain => 'Play again';
+
+  @override
+  String get kanjiNoStrokes => 'There\'s no stroke order for this character.';
+
+  @override
+  String get kanjiComponents => 'Components';
+
   @override
   String get aboutDictionaries => 'Dictionaries on this instance';