Polish iOS header glass and scroll-edge blur (#8097)

Wrap channel and DM titles in native glass and remove the
temporary-channel clock. Apply a soft status-area fade across iPhone
navigation, and fade the large title with scroll progress and fade in
the centered title, with Reduce Motion support.

Validation: mobile formatting/analysis and the full mobile suite passed.
Native iOS 26/27 simulator checks covered actual text opacity, header
resizing, quick reversal, and restored heading position; signed iPhone
build, installation, and launch succeeded. `just ci` was blocked by disk
exhaustion during Rust compilation.

---------

Signed-off-by: kenny lopez <klopez4212@gmail.com>

mobile/test/shared/widgets/frosted_app_bar_test.dart

@@ -10,6 +10,34 @@ import 'package:flutter_test/flutter_test.dart';
 import 'package:hooks_riverpod/hooks_riverpod.dart';
 
 void main() {
+  testWidgets('iOS conversations request a backdrop before scrolling', (
+    tester,
+  ) async {
+    debugDefaultTargetPlatformOverride = TargetPlatform.iOS;
+    addTearDown(() => debugDefaultTargetPlatformOverride = null);
+    await tester.pumpWidget(
+      ProviderScope(
+        child: MaterialApp(
+          theme: AppTheme.light(),
+          home: const Stack(
+            children: [
+              FrostedAppBar(
+                title: Text('Alice'),
+                nativeSubtitle: 'Online',
+                alwaysFrosted: true,
+              ),
+            ],
+          ),
+        ),
+      ),
+    );
+    final view = tester.widget<UiKitView>(find.byType(UiKitView));
+    expect(view.creationParams, containsPair('alwaysFrosted', true));
+    expect(view.creationParams, containsPair('subtitle', 'Online'));
+    await tester.pumpWidget(const SizedBox());
+    debugDefaultTargetPlatformOverride = null;
+  });
+
   testWidgets(
     'conversation backdrop stays mounted across scroll and keyboard changes',
     (tester) async {