fix: prevent duplicate conversations from self-messages and relay backfill

- Add message deduplication using Set to track processed message IDs
- Filter out self-messages where sender = recipient
- Prevents duplicate conversation entries from:
  * Same message arriving from cache AND real-time subscription
  * Self-directed messages creating spurious conversations
- Ensures normal sent messages still appear in recipient conversations
- Reduces conversation count from 8 to 7 (removes duplicate)

Fixes issue where fast cache loading (0.5ms) creates race condition
with real-time subscription receiving backfill messages already in cache.

Author: psam21

src/hooks/useConversations.ts

@@ -21,6 +21,7 @@ export const useConversations = () => {
   const [conversations, setConversations] = useState<Conversation[]>([]);
   const [isLoading, setIsLoading] = useState(true);
   const [error, setError] = useState<string | null>(null);
+  const [processedMessageIds] = useState<Set<string>>(new Set());
 
   /**
    * Load conversations from relays
@@ -91,6 +92,27 @@ export const useConversations = () => {
       isSent: message.isSent,
     });
 
+    // Deduplication: Skip if we've already processed this message
+    if (processedMessageIds.has(message.id)) {
+      console.log('[useConversations] ⏭️  Skipping duplicate message', {
+        id: message.id?.substring(0, 8),
+      });
+      return;
+    }
+    
+    // Filter out self-messages: Skip if sender = recipient (message to self)
+    if (message.senderPubkey === message.recipientPubkey) {
+      console.log('[useConversations] 🚫 Skipping self-message (sender = recipient)', {
+        id: message.id?.substring(0, 8),
+        pubkey: message.senderPubkey?.substring(0, 8),
+      });
+      processedMessageIds.add(message.id); // Mark as processed to avoid checking again
+      return;
+    }
+    
+    // Mark message as processed
+    processedMessageIds.add(message.id);
+    
     const otherPubkey = message.isSent ? message.recipientPubkey : message.senderPubkey;
     let updatedConversation: Conversation | undefined;
 
@@ -173,7 +195,7 @@ export const useConversations = () => {
         });
       }
     }
-  }, []);  /**
+  }, [processedMessageIds]);  /**
    * Subscribe to new messages for real-time updates
    */
   useEffect(() => {