fix: improve chat message deduplication, add conversation refresh logic, and update UI components for consistency

lib/features/messaging/presentation/providers/messaging_provider.dart

@@ -585,6 +585,24 @@ class MessagingNotifier extends StateNotifier<MessagingState> {
     }
   }
 
+  /// Refetch a single conversation — used when opening chat to get fresh
+  /// presence (isOnline/lastSeenAt) since the list may be stale. Mirrors
+  /// web's selectConversation which calls getConversation on open.
+  Future<void> refreshConversation(String conversationId) async {
+    try {
+      final fresh = await _repository.getConversation(conversationId);
+      if (!mounted) return;
+      final updated = state.conversations.map((c) {
+        return c.id == conversationId
+            ? c.copyWith(otherParty: fresh.otherParty)
+            : c;
+      }).toList();
+      state = state.copyWith(conversations: updated);
+    } catch (_) {
+      // Non-fatal — existing cached data remains in place
+    }
+  }
+
   Future<void> loadUnreadCount() async {
     try {
       final count = await _repository.getUnreadCount();