Document refuel beep as seek+Play() on each Update()

Author: morozov

spec/14-sound.md

@@ -59,10 +59,15 @@ A rising-pitch jingle that plays over 64 frames (~1.3 seconds) when
 `ControlFlags.BonusLife` is set. Uses the ROM BEEPER routine with decreasing pitch values
 (7 → 0), producing a sound that rises in frequency over time.
 
-### Refueling Beep (One-Shot)
+### Refueling Beep (One-Shot per Frame)
 
-A short high-pitched beep played each frame while the plane is actively receiving fuel.
-Uses ROM BEEPER. Only plays when the plane is flying straight (not banking).
+A short high-pitched beep (~14.6 ms) played once per game frame while the plane is
+actively receiving fuel. Uses ROM BEEPER. Only plays when the plane is flying straight
+(not banking).
+
+In Ebiten: seek the player to the start and call `Play()` on each `Update()` while
+refueling is active. The beep finishes well before the next frame (~67–83 ms), so there
+is no overlap.
 
 ### Tank Full (One-Shot)