fix(ui): floating buttons stay put while the keyboard is up

A screen making way for the keyboard had its floating buttons lifted
above it, where they stood over what was typed, such as the Library's
search results. They now stay where they stand, behind the keyboard.

Whats-New: The buttons at the foot of a screen no longer rise with the keyboard.
Whats-New-De: Die Knöpfe am Fuß eines Bildschirms steigen nicht mehr mit der Tastatur.

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

packages/halkyon_ui/test/widget/navigation_frame_test.dart

@@ -299,6 +299,19 @@ void main() {
     expect(tester.getRect(find.byType(FloatingActionButton)), before);
   });
 
+  testWidgets('the button stays where it stands, behind the keyboard, on a '
+      'screen that makes way for it (a search in the Library)', (tester) async {
+    await showPhone(tester, fadingScreen());
+    await tester.pumpAndSettle();
+    final before = tester.getRect(find.byType(FloatingActionButton));
+
+    tester.view.viewInsets = const FakeViewPadding(bottom: 300);
+    addTearDown(tester.view.resetViewInsets);
+    await tester.pumpAndSettle();
+
+    expect(tester.getRect(find.byType(FloatingActionButton)), before);
+  });
+
   testWidgets("a screen without its own fade keeps the frame's", (
     tester,
   ) async {