feat(tui/input): map Ctrl+Backspace to delete current line in composer

Provide a portable shortcut for deleting the entire current line when
terminals don’t forward the Command/SUPER modifier (e.g., iTerm2). This
mirrors Cmd+Backspace behavior where supported, without affecting existing
Alt+Backspace (word delete) and Ctrl+H (backspace) bindings.

codex-rs/tui/src/bottom_pane/textarea.rs

@@ -253,6 +253,16 @@ impl TextArea {
             } if modifiers == (KeyModifiers::CONTROL | KeyModifiers::ALT) => {
                 self.delete_backward_word()
             },
+            KeyEvent {
+                code: KeyCode::Backspace,
+                modifiers: KeyModifiers::CONTROL,
+                ..
+            } => {
+                // Map Ctrl+Backspace to delete the entire current line contents.
+                // This provides a portable shortcut similar to macOS Cmd+Backspace
+                // for terminals that do not forward the Command (SUPER) modifier.
+                self.delete_entire_line();
+            }
             KeyEvent {
                 code: KeyCode::Backspace,
                 modifiers: KeyModifiers::ALT,