tui: support Ghostty Ctrl-b/Ctrl-f fallback (#2427)

Ensure Emacs-style Ctrl-b/Ctrl-f work when terminals send bare control
chars.

- Map ^B (U+0002) to move left when no CONTROL modifier is reported.
- Map ^F (U+0006) to move right when no CONTROL modifier is reported.
- Preserve existing Ctrl-b/Ctrl-f and Alt-b/Alt-f behavior.
- Add unit test covering the fallback path.

Background: Ghostty (and some tmux/terminal configs) can emit bare
control characters for Ctrl-b/Ctrl-f. Previously these could be treated
as literal input; with this change both styles behave identically.

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

@@ -204,6 +204,16 @@ impl TextArea {
 
     pub fn input(&mut self, event: KeyEvent) {
         match event {
+            // Some terminals (or configurations) send Control key chords as
+            // C0 control characters without reporting the CONTROL modifier.
+            // Handle common fallbacks for Ctrl-B/Ctrl-F here so they don't get
+            // inserted as literal control bytes.
+            KeyEvent { code: KeyCode::Char('\u{0002}'), modifiers: KeyModifiers::NONE, .. } /* ^B */ => {
+                self.move_cursor_left();
+            }
+            KeyEvent { code: KeyCode::Char('\u{0006}'), modifiers: KeyModifiers::NONE, .. } /* ^F */ => {
+                self.move_cursor_right();
+            }
             KeyEvent {
                 code: KeyCode::Char(c),
                 // Insert plain characters (and Shift-modified). Do NOT insert when ALT is held,
@@ -1142,6 +1152,25 @@ mod tests {
         assert_eq!(t.cursor(), 1);
     }
 
+    #[test]
+    fn control_b_f_fallback_control_chars_move_cursor() {
+        use crossterm::event::KeyCode;
+        use crossterm::event::KeyEvent;
+        use crossterm::event::KeyModifiers;
+
+        let mut t = ta_with("abcd");
+        t.set_cursor(2);
+
+        // Simulate terminals that send C0 control chars without CONTROL modifier.
+        // ^B (U+0002) should move left
+        t.input(KeyEvent::new(KeyCode::Char('\u{0002}'), KeyModifiers::NONE));
+        assert_eq!(t.cursor(), 1);
+
+        // ^F (U+0006) should move right
+        t.input(KeyEvent::new(KeyCode::Char('\u{0006}'), KeyModifiers::NONE));
+        assert_eq!(t.cursor(), 2);
+    }
+
     #[test]
     fn cursor_vertical_movement_across_lines_and_bounds() {
         let mut t = ta_with("short\nloooooooooong\nmid");