Harpy: flight stamina cost actually works now

• The stamina cost added in 1.1.1 never had any real effect: it wrote directly to saturation, but

• vanilla only ever drops the visible hunger bar once saturation is already at 0, which is where it

• sits most of the time anyway, making the whole feature silently do nothing.

• Reworked to charge hunger while she's actively gaining speed in flight, routed through vanilla's

• real exhaustion pipeline. Steady gliding/coasting still costs nothing, no matter how long it lasts.

• Small hotfix, no other changes.