chore: Add floating action button for adding client hubs

Replaces the primary button for adding hubs with a floating action button and sets the background color of the Scaffold. This improves the UI by providing a more standard and accessible way to add new hubs.

apps/mobile/packages/features/client/hubs/lib/src/presentation/pages/client_hubs_page.dart

@@ -46,8 +46,18 @@ class ClientHubsPage extends StatelessWidget {
         },
         builder: (context, state) {
           return Scaffold(
+            backgroundColor: UiColors.bgMenu,
+            floatingActionButton: FloatingActionButton(
+              onPressed: () => BlocProvider.of<ClientHubsBloc>(
+                context,
+              ).add(const ClientHubsAddDialogToggled(visible: true)),
+              shape: const RoundedRectangleBorder(
+                borderRadius: BorderRadius.all(Radius.circular(8)),
+              ),
+              child: const Icon(UiIcons.add),
+            ),
             body: Stack(
-              children: [
+              children: <Widget>[
                 CustomScrollView(
                   slivers: [
                     _buildAppBar(context),
@@ -185,17 +195,6 @@ class ClientHubsPage extends StatelessWidget {
                       ),
                     ],
                   ),
-                  UiButton.primary(
-                    onPressed: () => BlocProvider.of<ClientHubsBloc>(
-                      context,
-                    ).add(const ClientHubsAddDialogToggled(visible: true)),
-                    text: t.client_hubs.add_hub,
-                    leadingIcon: UiIcons.add,
-                    style: ElevatedButton.styleFrom(
-                      minimumSize: const Size(0, 40),
-                      maximumSize: const Size.fromHeight(40),
-                    ),
-                  ),
                 ],
               ),
             ],