Add directional conversation focus shortcuts in workspace mode (#59287)

## What changed

- Add configurable `focus_pane_left` and `focus_pane_right` actions, defaulting to `leader left` / `leader h` and `leader right` / `leader l`.
- Move focus to the parent or open side conversation without reopening a hidden pane. Preserve the current interaction when no neighbor is available, and accept fresh typing after a no-op shortcut while suppressing reported key repeats.
- Expose the actions in the keymap picker and configuration schema, and prevent workspace-only pane bindings from claiming keys in classic mode.

## Testing

Add regression coverage for pane navigation, preserved transcript selection and search, fresh typing after a no-op, key capture, and binding conflicts and limits.

GitOrigin-RevId: 7f7629d15cffcd35d1353b36c5c9208dbb1034e8

codex-rs/tui/src/transcript_view_tests.rs

@@ -1314,6 +1314,7 @@ fn user_prompt_has_a_background_without_a_terminal_palette() {
 #[test]
 fn spoken_prompt_selection_keeps_its_fallback_contrast() {
     use crate::history_cell::new_spoken_user_prompt;
+    use crate::terminal_palette::rgb_color;
     use ratatui::style::Color;
     use ratatui::style::Modifier;
 
@@ -1352,8 +1353,8 @@ fn spoken_prompt_selection_keeps_its_fallback_contrast() {
                     (
                         Some("one\n"),
                         Color::Red,
-                        Color::Rgb(238, 238, 238),
-                        Color::Rgb(68, 68, 68),
+                        rgb_color((238, 238, 238)),
+                        rgb_color((68, 68, 68)),
                         true
                     )
                 );