fix(card): a search for blue no longer finds blunt

The card browser looked for a query also with every ae, oe and ue made
a, o and u, so that maedchen found Mädchen: in any language, so blue
found blunt, Spanish que found aquí, and ue nearly everything. A card's
umlauts are written out on its side instead, beside its folded text,
and a query is matched as typed.

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

@@ -5,7 +5,7 @@ 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);
+        matchesQuery(searchableText(text), query);
 
     expect(finds('Straße', 'strasse'), isTrue);
     expect(finds('Mädchen', 'madchen'), isTrue);
@@ -18,6 +18,11 @@ void main() {
     expect(finds('たべる', 'taberu'), isTrue);
     expect(finds('テレビ', 'てれび'), isTrue);
     expect(finds('Haus', 'maus'), isFalse);
+    // Only a card's umlauts are written out, never a query's ue, oe or ae.
+    expect(finds('Müller', 'mueller'), isTrue);
+    expect(finds('blunt', 'blue'), isFalse);
+    expect(finds('aquí', 'que'), isFalse);
+    expect(finds('god', 'goed'), isFalse);
   });
 
   test('A–Z compares letters as their bare ones: Ärger among the a, xué '