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/models.rs

@@ -129,5 +129,6 @@ pub struct SessionTab {
     pub search: SearchState,
     pub log_enabled: bool,
     pub log_path: String,
+    pub show_sent: bool,
     pub log_writer: Option<LogWriter>,
 }