Swarm Drones

Explosion sound remastering: Stretch and layer the same low-frequency material to create about 0.8 seconds of rumbling tail, with mid-section energy at 7 dB, overall average from −20.1 dB → −15.7 dB, and peak still leaving 2.8 dB headroom (no clipping, no blurring).

Delete the second overlapping explosion layer at the moment of release (ELYTRA_FLYING / LIGHTNING_BOLT_THUNDER): When the mother ship passes overhead, it naturally triggers one explosion of the same type; having two layers together just suppresses the ones that explode first.

Mother ship engine rumble playback interval: 1.5 s → 3 s (aligned with 3-second audio), no longer self-layering, removing the continuous low-frequency wall about 8 dB louder than the explosion.

Fix the issue where the swarm_grow overture plays in the Overworld: The first 5 seconds cannot be heard when summoned in the Nether / End.