Addresses an issue where commands prefixed with `!` (e.g., `!ls`) were incorrectly handled by the shell command processor if the `!` was added after initially typing the command.\n- Ensures that such commands are correctly forwarded to the Gemini model.\n- Updates `useGeminiStream` to be aware of shell mode to properly manage streaming state.\n\nFixes https://buganizer.corp.google.com/issues/418761305