SwitchToPreviousImeTool
Switches the active keyboard back to the user's previous IME via InputMethodService.switchToPreviousInputMethod. Unlike the other IME tools this only needs the service bound (not necessarily an editor focused), so the LLM can hand control back even without a live input connection. Returns an error if the service isn't bound, or if the system rejects the switch (e.g. no previous IME recorded).