fix: improve response timeout error message with user-friendly description

Replace generic 'Response timeout' message with a more descriptive error
that explains the provider may be overloaded or there's an internet
connection/proxy issue when communicating with the provider.

Updated in:
- streaming.rs (2 occurrences)
- subagent.rs (1 occurrence)

Author: echobt

src/cortex-tui/src/runner/event_loop/streaming.rs

@@ -285,7 +285,7 @@ impl EventLoop {
                     Err(_) => {
                         // Timeout
                         let _ = tx
-                            .send(StreamEvent::Error("Response timeout".to_string()))
+                            .send(StreamEvent::Error("The provider appears to be overloaded or your internet connection/proxy is experiencing issues communicating with it.".to_string()))
                             .await;
                         break;
                     }
@@ -833,7 +833,7 @@ impl EventLoop {
                     }
                     Err(_) => {
                         let _ = tx
-                            .send(StreamEvent::Error("Response timeout".to_string()))
+                            .send(StreamEvent::Error("The provider appears to be overloaded or your internet connection/proxy is experiencing issues communicating with it.".to_string()))
                             .await;
                         break;
                     }

src/cortex-tui/src/runner/event_loop/subagent.rs

@@ -314,7 +314,7 @@ impl EventLoop {
                                 .send(ToolEvent::Failed {
                                     id: id.clone(),
                                     name: "Task".to_string(),
-                                    error: "Response timeout".to_string(),
+                                    error: "The provider appears to be overloaded or your internet connection/proxy is experiencing issues communicating with it.".to_string(),
                                     duration: started_at.elapsed(),
                                 })
                                 .await