Open the agents overview from an empty composer (#41917)

## What changed

- Open the agents overview with Left from an empty, focused composer in local-daemon sessions.
- Keep the shortcut inactive while editing text, using transient input surfaces, or when Left has been explicitly remapped.
- Show the contextual shortcut in the footer and shortcuts overlay.
- Leave the configurable `open_agents` action unbound by default instead of assigning `Alt+A`.

## Testing

- Add coverage for session eligibility, input-state guards, editor and Vim remaps, event dispatch, and footer rendering.

GitOrigin-RevId: ef17db3d9d09c3a08c3f7353c5b8a02f2b61c696

codex-rs/tui/src/chatwidget/interaction.rs

@@ -4,6 +4,10 @@ use super::*;
 use crate::bottom_pane::BottomPaneView;
 
 impl ChatWidget {
+    pub(crate) fn set_agents_navigation_enabled(&mut self, enabled: bool) {
+        self.bottom_pane.set_agents_navigation_enabled(enabled);
+    }
+
     pub(crate) fn keymap_contexts(&self) -> crate::keymap::KeymapContextSet {
         self.bottom_pane.keymap_contexts()
     }