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/test/feature/kanji/model/hangul_test.dart

@@ -0,0 +1,26 @@
+import 'package:flutter_test/flutter_test.dart';
+import 'package:halkyon_learn_flutter/src/feature/kanji/model/hangul.dart';
+
+void main() {
+  test('a Hangul syllable is written with its letters: the opening '
+      'consonant, the vowel and the closing one or cluster', () {
+    expect(hangulLetters('가'), ['ㄱ', 'ㅏ']);
+    expect(hangulLetters('닭'), ['ㄷ', 'ㅏ', 'ㄺ']);
+    expect(hangulLetters('쓰'), ['ㅆ', 'ㅡ']);
+    expect(hangulLetters('왜'), ['ㅇ', 'ㅙ']);
+    expect(hangulLetters('힣'), ['ㅎ', 'ㅣ', 'ㅎ']);
+    // What is no syllable stays as it is.
+    expect(hangulLetters('ㄱ'), ['ㄱ']);
+    expect(hangulLetters('食'), ['食']);
+  });
+
+  test('scripts whose strokes are drawn: Han characters, kana, Hangul; '
+      'not the alphabets', () {
+    expect(hasDrawnScript('食べる'), isTrue);
+    expect(hasDrawnScript('学习'), isTrue);
+    expect(hasDrawnScript('학교'), isTrue);
+    expect(hasDrawnScript('ㄱ'), isTrue);
+    expect(hasDrawnScript('das Haus'), isFalse);
+    expect(hasDrawnScript('Β β'), isFalse);
+  });
+}

apps/learn/halkyon_learn_flutter/test/feature/kanji/model/radical_test.dart

@@ -0,0 +1,57 @@
+import 'package:flutter_test/flutter_test.dart';
+import 'package:halkyon_learn_flutter/src/feature/kanji/model/radical.dart';
+
+void main() {
+  test('the 214 Kangxi radicals in their order, by their strokes from 1 '
+      'to 17', () {
+    expect(
+      [for (final radical in radicals) radical.number],
+      [
+        for (var number = 1; number <= 214; number++) number,
+      ],
+    );
+    final strokes = [for (final radical in radicals) radical.strokes];
+    expect(strokes, orderedEquals([...strokes]..sort()));
+    expect((strokes.first, strokes.last), (1, 17));
+    // Const, as the table is: a record compares its lists by identity.
+    expect(radicals[84], const (
+      number: 85,
+      character: '水',
+      variants: ['氵'],
+      strokes: 4,
+      name: 'water',
+    ));
+  });
+
+  test('each is one character, as is every form it takes in kanji', () {
+    for (final radical in radicals) {
+      for (final form in [radical.character, ...radical.variants]) {
+        expect(form.runes, hasLength(1), reason: '${radical.number}');
+      }
+    }
+  });
+
+  test("a radical's label is the dictionary's", () {
+    expect(radicalLabel(85), 'radical:85');
+  });
+
+  test('the forms a radical takes in each language: simplified Chinese its '
+      "own, traditional Chinese and Korean without Japanese's own", () {
+    final speech = radicals[148];
+    final dragon = radicals[211];
+    final food = radicals[183];
+    expect(radicalFormsIn(speech, 'zh-Hans'), ['讠']);
+    expect(radicalFormsIn(speech, 'zh-Hant'), isEmpty);
+    expect(radicalFormsIn(dragon, 'ja'), ['竜']);
+    expect(radicalFormsIn(dragon, 'zh'), ['龙']);
+    expect(radicalFormsIn(dragon, 'ko'), isEmpty);
+    // Simplified Chinese writes 食 as 饣 at a character's side, not 飠.
+    expect(radicalFormsIn(food, 'zh-CN'), ['饣']);
+    expect(radicalFormsIn(food, 'zh-TW'), ['飠']);
+    expect(radicalsIn('zh-Hans')[148].variants, ['讠']);
+    // Each form once, never the radical itself.
+    expect(radicalFormsIn(radicals[198], 'zh'), ['麦']);
+    expect(radicalFormsIn(radicals[202], 'zh'), isEmpty);
+    expect((hasRadicals('ko'), hasRadicals('el')), (true, false));
+  });
+}