The fan-speed endpoint always reported 'Chamber fan set to N%', so on
P2S/X2D — where the printer card labels that fan 'Exhaust' — clicking
Exhaust produced a toast saying Chamber fan.
Adds uses_exhaust_fan_label() to printer_models so the badge label and the
API response share one source of truth, and uses it to pick 'Exhaust fan'
vs 'Chamber fan' in the response message.
Tests: helper coverage for P2S/X2D (incl. internal codes N7/N6), other
enclosed models, and unknown/missing model; API test asserting the message
matches the badge label per model.