The Vulcan gets its true voice e55e9d1

The gatling sample is rebuilt to match the real M61: a 100-rounds-per-second burst synthesized from scratch — powder-crack impulse train, mechanical roar, and the fire-rate ripple that gives the Vulcan its buzzsaw shriek. YouTube was unreachable from the build sandbox, so the sound is synthesized to the reference rather than lifted from the video.