Add missing routing asset warning

lib/features/geo_asset/overview/geo_assets_overview_page.dart

@@ -3,6 +3,7 @@ import 'package:hiddify/core/localization/translations.dart';
 import 'package:hiddify/features/geo_asset/overview/geo_assets_overview_notifier.dart';
 import 'package:hiddify/features/geo_asset/widget/geo_asset_tile.dart';
 import 'package:hooks_riverpod/hooks_riverpod.dart';
+import 'package:sliver_tools/sliver_tools.dart';
 
 class GeoAssetsOverviewPage extends HookConsumerWidget {
   const GeoAssetsOverviewPage({super.key});
@@ -17,6 +18,7 @@ class GeoAssetsOverviewPage extends HookConsumerWidget {
         slivers: [
           SliverAppBar(
             title: Text(t.settings.geoAssets.pageTitle),
+            pinned: true,
             actions: [
               PopupMenuButton(
                 itemBuilder: (context) {
@@ -34,6 +36,17 @@ class GeoAssetsOverviewPage extends HookConsumerWidget {
               ),
             ],
           ),
+          if (state case AsyncData(value: final geoAssets))
+            SliverPinnedHeader(
+              child: AnimatedSwitcher(
+                duration: const Duration(milliseconds: 200),
+                child: geoAssets
+                        .where((e) => e.$1.active && e.$2 == null)
+                        .isNotEmpty
+                    ? const MissingRoutingAssetsCard()
+                    : const SizedBox(),
+              ),
+            ),
           switch (state) {
             AsyncData(value: final geoAssets) => SliverList.builder(
                 itemBuilder: (context, index) {
@@ -54,3 +67,39 @@ class GeoAssetsOverviewPage extends HookConsumerWidget {
     );
   }
 }
+
+class MissingRoutingAssetsCard extends HookConsumerWidget {
+  const MissingRoutingAssetsCard({super.key});
+
+  @override
+  Widget build(BuildContext context, WidgetRef ref) {
+    final t = ref.watch(translationsProvider);
+
+    return Card(
+      margin: const EdgeInsets.symmetric(
+        horizontal: 12,
+        vertical: 4,
+      ),
+      child: Row(
+        children: [
+          const Padding(
+            padding: EdgeInsets.all(8.0),
+            child: Icon(Icons.lightbulb),
+          ),
+          Expanded(
+            child: Column(
+              crossAxisAlignment: CrossAxisAlignment.stretch,
+              children: [
+                Padding(
+                  padding:
+                      const EdgeInsets.symmetric(horizontal: 8, vertical: 8),
+                  child: Text(t.settings.geoAssets.missingGeoAssetsMsg),
+                ),
+              ],
+            ),
+          ),
+        ],
+      ),
+    );
+  }
+}