feat(card): the card browser finds and sorts words of any language as typed

Search folded case and katakana only, for Japanese. It now also leaves out
accents, tone marks and umlauts (strasse finds Straße, maedchen and
madchen Mädchen, σπιτι σπίτι, xue xi xué xí), and A–Z sorts by the same
bare letters, so Ärger stands among the a's.

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

halkyon_learn_flutter/test/feature/card/model/card_browser_test.dart

@@ -0,0 +1,29 @@
+import 'package:flutter_test/flutter_test.dart';
+import 'package:halkyon_learn_flutter/src/feature/card/model/card_browser.dart';
+
+void main() {
+  test('a search finds words of any language as typed on any keyboard: '
+      'without accents, tone marks or umlauts, ß as ss, kana by romaji', () {
+    bool finds(String text, String query) =>
+        matchesQuery(searchFolded(text), query);
+
+    expect(finds('Straße', 'strasse'), isTrue);
+    expect(finds('Mädchen', 'madchen'), isTrue);
+    expect(finds('Mädchen', 'maedchen'), isTrue);
+    expect(finds('το σπίτι', 'σπιτι'), isTrue);
+    expect(finds('ο δρόμος', 'δρομος'), isTrue);
+    expect(finds('xué xí', 'xue xi'), isTrue);
+    expect(finds('nǚ ér', 'nu er'), isTrue);
+    expect(finds('café', 'CAFE'), isTrue);
+    expect(finds('たべる', 'taberu'), isTrue);
+    expect(finds('テレビ', 'てれび'), isTrue);
+    expect(finds('Haus', 'maus'), isFalse);
+  });
+
+  test('A–Z compares letters as their bare ones: Ärger among the a, xué '
+      'beside xue', () {
+    expect(searchFolded('Ärger'), 'arger');
+    expect(searchFolded('xué'), 'xue');
+    expect(searchFolded('ὁδός'), 'οδοσ');
+  });
+}