Phase 7A / 0.0.18.10 - airborne meteor flight-audio range tune

Baseline: 0.0.18.9 user-confirmed working.

Only airborne meteor flight-audio reach changed:
- SoundEvent fixed range: 256 -> 768 blocks
- meteor_flight_1..4 attenuation_distance: 256 -> 768
- same user-approved sound assets
- same 8-tick moving emission cadence
- same volume/pitch
- same positional source at the meteor entity
- impact audio and all gameplay/UI/visual systems unchanged

Maintenance rule:
Always update both the registered SoundEvent fixed range and sounds.json attenuation_distance
together when changing this range.
