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/lib/src/feature/card/model/card_browser.dart

@@ -109,7 +109,7 @@ typedef BrowsedCard = ({
 /// `たべる` finds た.べる).
 String searchTextOf(Card card, List<Tag> tags) {
   final content = card.content;
-  return searchFolded(
+  return searchableText(
     [
       content.front.plainText,
       content.back.plainText,
@@ -126,6 +126,26 @@ String searchTextOf(Card card, List<Tag> tags) {
   );
 }
 
+/// [text] as a card's search text holds it: folded ([searchFolded]), and
+/// where it has German's umlauts, folded once more with them written out,
+/// so `maedchen` finds Mädchen as `madchen` does. Written out on the card's
+/// side, not the query's: a query's own `ue` stays as typed, and `blue`
+/// doesn't find blunt, nor Spanish `que` aquí.
+String searchableText(String text) {
+  final folded = searchFolded(text);
+  final lower = text.toLowerCase();
+  if (!lower.contains(_umlaut)) {
+    return folded;
+  }
+  final written = lower
+      .replaceAll('ä', 'ae')
+      .replaceAll('ö', 'oe')
+      .replaceAll('ü', 'ue');
+  return '$folded\n${searchFolded(written)}';
+}
+
+final _umlaut = RegExp('[äöü]');
+
 /// [text] as searches compare it and A–Z orders it: in lower case,
 /// katakana as hiragana, without accents and tone marks (Latin and Greek
 /// letters, pinyin's vowels), ß as ss and Greek's final sigma as σ; so
@@ -177,18 +197,14 @@ final _bare = {
 };
 
 /// Whether a card whose [searchText] is [searchTextOf] holds [query]: as
-/// typed, with German's umlauts written out as typed without them
-/// (`maedchen` finds Mädchen), or romaji typed for its kana (`taberu`
-/// finds たべる).
+/// typed (German's umlauts written out or not, see [searchableText]), or
+/// romaji typed for its kana (`taberu` finds たべる).
 bool matchesQuery(String searchText, String query) {
   final typed = searchFolded(query.trim());
   if (typed.isEmpty) {
     return true;
   }
   return searchText.contains(typed) ||
-      searchText.contains(
-        typed.replaceAll('ae', 'a').replaceAll('oe', 'o').replaceAll('ue', 'u'),
-      ) ||
       searchText.contains(romajiToHiragana(typed, finished: true));
 }
 

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 '