Implement indefinite store-and-forward for favorite peers

- Change message cache timeout from 5 minutes to 12 hours for regular peers
- Add indefinite message storage for favorite peers with 1000 message limit
- Cache relayed messages for offline favorites
- Automatically send cached messages when favorites come online
- Use public key fingerprints to identify favorites persistently
- Add isFavorite delegate method to check favorites by fingerprint

bitchat/ViewModels/ChatViewModel.swift

@@ -652,4 +652,8 @@ extension ChatViewModel: BitchatDelegate {
         return Array(Set(mentions)) // Remove duplicates
     }
     
+    func isFavorite(fingerprint: String) -> Bool {
+        return favoritePeers.contains(fingerprint)
+    }
+    
 }