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/pubspec.yaml

@@ -76,6 +76,8 @@ dependencies:
   material_ui: ^1.5.0
   package_info_plus: ^10.2.2
   path: ^1.9.1
+  # SVG path data, for the strokes KanjiVG draws characters with.
+  path_parsing: ^1.1.0
   path_provider: ^2.1.6
   # Modern Anki packages are zstd-compressed, every frame without its content
   # size, which upstream's v1.0.0 refuses. Our fork decodes them, pinned to a
@@ -150,6 +152,8 @@ flutter:
     # The bundled fonts' licences, for the licence list (see assets/fonts/ATTRIBUTION.md).
     - assets/fonts/OFL-NotoSans.txt
     - assets/fonts/OFL-NotoSansCJK.txt
+    # How kanji and kana are written, from KanjiVG (see assets/kanjivg/ATTRIBUTION.md).
+    - assets/kanjivg/
 
   # The app's own fonts, the same on every device and never fetched: Noto Sans for
   # Latin, Greek and Cyrillic; behind it Noto Sans JP, SC, TC and KR for Japanese,