feat: implement mobile UI, Android build configuration, and share intent handling using share_handler

lib/features/sender/presentation/providers/share_handler_provider.dart

@@ -0,0 +1,31 @@
+import 'package:flutter_riverpod/flutter_riverpod.dart';
+import 'package:share_handler/share_handler.dart';
+import 'sender_providers.dart';
+
+final shareHandlerProvider = Provider<void>((ref) {
+  final handler = ShareHandler.instance;
+  
+  // Listen for background shares
+  handler.sharedMediaStream.listen((SharedMedia media) {
+    _handleMedia(media, ref);
+  });
+
+  // Check for initial share (app opened via share)
+  handler.getInitialSharedMedia().then((media) {
+    if (media != null) {
+      _handleMedia(media, ref);
+    }
+  });
+  
+  return;
+});
+
+void _handleMedia(SharedMedia media, Ref ref) {
+  final content = media.content;
+  if (content != null && content.isNotEmpty) {
+    // If it's a URL or contains a URL, send it
+    if (content.startsWith('http')) {
+       ref.read(senderProvider.notifier).sendLink(content);
+    }
+  }
+}

lib/features/sender/presentation/screens/mobile_sender_screen.dart

@@ -3,6 +3,7 @@ import 'package:flutter_riverpod/flutter_riverpod.dart';
 import '../../../../core/theme/app_colors.dart';
 import '../../../discovery/presentation/providers/discovery_providers.dart';
 import '../providers/sender_providers.dart';
+import '../providers/share_handler_provider.dart';
 
 class MobileSenderScreen extends ConsumerStatefulWidget {
   const MobileSenderScreen({super.key});
@@ -14,6 +15,11 @@ class MobileSenderScreen extends ConsumerStatefulWidget {
 class _MobileSenderScreenState extends ConsumerState<MobileSenderScreen> {
   final _urlController = TextEditingController();
 
+  @override
+  void initState() {
+    super.initState();
+  }
+
   @override
   void dispose() {
     _urlController.dispose();
@@ -22,6 +28,9 @@ class _MobileSenderScreenState extends ConsumerState<MobileSenderScreen> {
 
   @override
   Widget build(BuildContext context) {
+    // Initialize share handler
+    ref.watch(shareHandlerProvider);
+    
     final devicesAsync = ref.watch(discoveredDevicesProvider);
     final senderState = ref.watch(senderProvider);