feat(gui): add 'Show sent data' toggle in send panel

Add checkbox to control whether sent text/hex appears in the
console/hex view. Default enabled (current behavior). Log-to-file
is unaffected.

crates/pipeview-gui/src/app.rs

@@ -280,6 +280,7 @@ impl XserialApp {
             search: SearchState::default(),
             log_enabled: false,
             log_path: String::new(),
+            show_sent: true,
             log_writer: None,
         });
     }