Fix retry button blocked by overly broad "exist" filter (#12397)

The retry logic was blocking retry buttons for errors containing "exist", 
which incorrectly filtered out "An existing connection was forcibly closed" 
network errors. Changed to "not exist" to only block "ID does not exist" 
type errors while allowing legitimate network disconnection errors to show 
retry buttons.

Fixes issue where users couldn't retry after network disconnections.

src/client.rs

@@ -3693,7 +3693,7 @@ pub fn check_if_retry(msgtype: &str, title: &str, text: &str, retry_for_relay: b
         && title == "Connection Error"
         && ((text.contains("10054") || text.contains("104")) && retry_for_relay
             || (!text.to_lowercase().contains("offline")
-                && !text.to_lowercase().contains("exist")
+                && !text.to_lowercase().contains("not exist")
                 && !text.to_lowercase().contains("handshake")
                 && !text.to_lowercase().contains("failed")
                 && !text.to_lowercase().contains("resolve")