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_curator/test/alphabets_test.dart

@@ -0,0 +1,45 @@
+import 'dart:convert';
+
+import 'package:halkyon_learn_curator/src/sources/alphabets.dart';
+import 'package:test/test.dart';
+
+void main() {
+  test('the Greek alphabet in its order, each letter with its capital, '
+      'names, transliteration and sound', () {
+    final [header, ...letters] = [
+      for (final line in greekAlphabet())
+        jsonDecode(line) as Map<String, Object?>,
+    ];
+
+    expect(header['source'], 'greek-alphabet');
+    expect(header['kind'], 'characters');
+    expect(header['language'], 'el');
+    expect(letters, hasLength(24));
+    expect(letters.first['headword'], 'Α α');
+    final sigma = letters.singleWhere((letter) => letter['id'] == 'σ');
+    expect(sigma['headword'], 'Σ σ ς');
+    expect(sigma['keys'], containsAll(['ς', 'σίγμα', 'sigma', 's']));
+    expect(letters[1]['entry'], {
+      'romaji': 'v',
+      'script': 'greek',
+      'name': 'βήτα',
+      'englishName': 'beta',
+      'sound': 'v',
+    });
+    // Found by a name typed without its accent.
+    expect(letters.last['keys'], contains('ωμεγα'));
+  });
+
+  test('the Hangul letters in the order schools teach them, found by sound '
+      'and name', () {
+    final letters = hangulEntries();
+
+    expect(letters, hasLength(40));
+    expect(letters.first.headword, 'ㄱ');
+    expect(letters.first.keys, containsAll(['ㄱ', '기역', 'g', 'k']));
+    // ㅇ is silent opening a syllable: no key for its sound there.
+    final ieung = letters.singleWhere((letter) => letter.id == 'ㅇ');
+    expect(ieung.keys, ['ㅇ', '이응', 'ng']);
+    expect(letters.last.headword, 'ㅢ');
+  });
+}