An 80-year-old woman with dementia and heart failure (ejection fraction 35%) is admitted with delirium secondary to a urinary tract infection. She becomes agitated and distressed, posing a risk to herself. Non-pharmacological measures have been attempted but are insufficient. According to NICE NG97 (Dementia), which medication is generally considered the first-line choice for short-term control of agitation or aggression in dementia, when essential?