fix(tests): remove stale search-toggle test and fix ink_sparkle shader crash

The 'tapping search icon shows search bar' test was stale: the SearchBar is
now permanently visible in AppBar.bottom, so both its assertions held before
any tap. Deleted it; the existing 'SearchBar is always visible in the AppBar'
test already covers the same intent.

Added NoSplash.splashFactory to the widget-test ThemeData to prevent Flutter
from loading the pre-compiled ink_sparkle.frag shader, which was built for an
older SDK version and caused an INVALID_ARGUMENT crash on Flutter 3.44.0.

Closes #486

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

test/widget/email_list_screen_test.dart

@@ -104,30 +104,6 @@ void main() {
       expect(find.byIcon(Icons.star), findsOneWidget);
     });
 
-    testWidgets('tapping search icon shows search bar', (tester) async {
-      await tester.pumpWidget(
-        buildApp(
-          initialLocation: '/accounts/acc-1/mailboxes/INBOX/emails',
-          overrides: [
-            accountRepositoryProvider.overrideWithValue(
-              FakeAccountRepository([kTestAccount]),
-            ),
-            mailboxRepositoryProvider.overrideWithValue(
-              FakeMailboxRepository(),
-            ),
-            emailRepositoryProvider.overrideWithValue(FakeEmailRepository()),
-          ],
-        ),
-      );
-      await tester.pumpAndSettle();
-
-      await tester.tap(find.byIcon(Icons.search));
-      await tester.pumpAndSettle();
-
-      expect(find.byType(TextField), findsOneWidget);
-      expect(find.text('Search…'), findsOneWidget);
-    });
-
     testWidgets('submitting a search query shows "No results" when empty', (
       tester,
     ) async {

test/widget/helpers.dart

@@ -580,6 +580,7 @@ Widget buildApp({
       theme: ThemeData(
         colorScheme: ColorScheme.fromSeed(seedColor: Colors.indigo),
         useMaterial3: true,
+        splashFactory: NoSplash.splashFactory,
       ),
       darkTheme: ThemeData(
         colorScheme: ColorScheme.fromSeed(
@@ -587,6 +588,7 @@ Widget buildApp({
           brightness: Brightness.dark,
         ),
         useMaterial3: true,
+        splashFactory: NoSplash.splashFactory,
       ),
     ),
   );