fix(mobile): polish Inbox controls and system notices (#8423)

Use Tabler `filter-2` in Inbox and keep the iOS filter button rounded
when its menu closes. Remove shaded containers from chat system notices
while preserving spacing, profile links, and reactions.

Validation: mobile formatting, analysis, full test suite, and iOS
Release build; independent review found no blockers. Kenny verified the
icon and menu dismissal on his iPhone.

---------

Signed-off-by: Terp <5856f6900e8e0a4e0ea1f4f8d2ee33e4753d2119bc122f94ecafc660b46c0511@buzz.block.builderlab.xyz>
Co-authored-by: Terp <5856f6900e8e0a4e0ea1f4f8d2ee33e4753d2119bc122f94ecafc660b46c0511@buzz.block.builderlab.xyz>

mobile/ios/Runner/IosNavigationBar.swift

@@ -623,6 +623,7 @@ private final class IosNavigationBarView: NSObject, FlutterPlatformView {
       let glass = UIGlassEffect(style: .regular)
       glass.isInteractive = true
       surface.effect = glass
+      surface.cornerConfiguration = .capsule()
     } else {
       surface.backgroundColor = controlBackground
     }
@@ -647,6 +648,16 @@ private final class IosNavigationBarView: NSObject, FlutterPlatformView {
         if let action = item.primaryAction { button.addAction(action, for: .touchUpInside) }
         button.menu = item.menu
         button.showsMenuAsPrimaryAction = item.menu != nil
+        if item.menu != nil {
+          // UIKit lifts the button itself for its menu transition, not the
+          // enclosing glass. Give that return target the same rounded shape.
+          if #available(iOS 26.0, *) {
+            button.cornerConfiguration = .capsule()
+          }
+          button.layer.cornerRadius = 22
+          button.layer.cornerCurve = .circular
+          button.clipsToBounds = true
+        }
         button.isEnabled = item.isEnabled
         button.accessibilityLabel = item.accessibilityLabel
         button.accessibilityValue = item.accessibilityValue

mobile/lib/features/activity/activity_page.dart

@@ -437,7 +437,7 @@ class ActivityPage extends HookConsumerWidget {
         nativeActions: [
           IosNavigationAction(
             label: 'Filter inbox',
-            symbol: 'line.3.horizontal.decrease',
+            icon: BuzzIcons.filter2,
             children: [
               for (final entry in _filterLabels.entries)
                 IosNavigationAction(

mobile/lib/features/channels/channel_detail_page/system_rows.dart

@@ -196,16 +196,12 @@ class _SystemMessageRow extends HookConsumerWidget {
                     alignment: isHuddle
                         ? Alignment.centerLeft
                         : Alignment.center,
-                    child: Container(
+                    child: Padding(
                       key: ValueKey('activity-card-${message.id}'),
                       padding: const EdgeInsets.symmetric(
                         horizontal: Grid.twelve,
                         vertical: Grid.xxs,
                       ),
-                      decoration: BoxDecoration(
-                        color: context.colors.onSurface.withValues(alpha: 0.06),
-                        borderRadius: BorderRadius.circular(Radii.container),
-                      ),
                       child: IntrinsicWidth(
                         child: groupedMembership != null
                             ? _MembershipSystemMessageContent(

mobile/lib/shared/theme/buzz_icons.dart

@@ -5,6 +5,9 @@ import 'package:flutter/widgets.dart';
 /// Semantic names preserve existing call sites; artwork matches buzz-app.
 /// Native iOS controls share Tabler artwork except Back and Close navigation.
 abstract final class BuzzIcons {
+  /// Tabler `filter-2`. Referenced from Dart so release icon pruning retains it.
+  static const filter2 = IconData(0x1014b, fontFamily: 'BuzzTabler');
+
   static const cornerUpLeft = IconData(0xeb77, fontFamily: 'BuzzTabler');
   static const droplet = IconData(0xea97, fontFamily: 'BuzzTabler');
 

mobile/test/shared/theme/tabler_icon_render_test.dart

@@ -45,6 +45,10 @@ void main() {
                   child: Column(
                     mainAxisSize: MainAxisSize.min,
                     children: [
+                      const ListTile(
+                        leading: Icon(BuzzIcons.filter2),
+                        title: Text('Filter inbox'),
+                      ),
                       const ListTile(
                         leading: Icon(BuzzIcons.archive),
                         title: Text('Archive'),