chore: Halkyon Learn moves into apps/learn

Its server, client, app and curator, and the tools that write its
assets (maps, Anki fixtures, icons), as they are; paths are fixed in
the commits that follow.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
Signed-off-by: Tizian 「ティツィアーン」 <raisondetredev@pm.me>

apps/learn/halkyon_learn_flutter/assets/makemeahanzi/ATTRIBUTION.md

@@ -0,0 +1,23 @@
+# Stroke data of Chinese characters
+
+The stroke files in this folder derive from **Make Me a Hanzi**
+(<https://github.com/skishore/makemeahanzi>), its data as of 2018-10-16
+(commit `618dbab`), by Shaunak Kishore:
+
+- the strokes from its `graphics.txt`, derived from the fonts Arphic PL KaitiM
+  GB and Arphic PL UKai, © 1999 Arphic Technology Co., Ltd., distributed under
+  the Arphic Public License (`ARPHICPL.TXT`, unaltered, as it asks);
+- the components from its `dictionary.txt`, derived from the Unihan database
+  (© Unicode, Inc.) and CJKlib, distributed under the GNU Lesser General Public
+  License, version 3 or later (`LGPL.txt`, with Unicode's notice, as Make Me a
+  Hanzi ships it).
+
+They are distributed under the same licences; the app's licence list shows
+both. `halkyon_learn_curator`'s `curate makemeahanzi` writes them (see its
+README), and each file says how and when it was changed (`notice`), as the
+Arphic Public License asks: every stroke is the line Make Me a Hanzi draws
+through its middle (its median), scaled into KanjiVG's 109 × 109 square with
+its y axis pointing down, without the outlines; a character's components are
+the first split of its decomposition (海: 氵, 每). They are an aggregate beside
+the app, never part of its code nor copied into cards: a card names its
+character, and the app draws it from these files.