feat: Allow Esc to exit shell mode

- Update InputPrompt.tsx to handle Esc key for exiting shell mode.
- Modify ShellModeIndicator.tsx to reflect the new keybinding.
Fixes https://buganizer.corp.google.com/issues/419087952

packages/cli/src/ui/components/InputPrompt.tsx

@@ -189,6 +189,10 @@ export const InputPrompt: React.FC<InputPromptProps> = ({
           return true;
         }
         if (key.escape) {
+          if (shellModeActive) {
+            setShellModeActive(false);
+            return;
+          }
           completion.resetCompletionState();
           return;
         }