PortalHeim_SG1 gate sounds: credits

The gate sounds in this folder are mixes of a few public-domain (CC0) recordings plus sounds
synthesized for this mod. tools/make_sounds.py in the source repository rebuilds them.

Recordings used (all CC0 / public domain, from OpenGameArt):
- "100 CC0 SFX #2" by rubberduck: https://opengameart.org/content/100-cc0-sfx-2
  (stones_02, lock_open_01, thunder_01, loop_ambient_03)
- "Metal Impact Sounds" by BMacZero (Brian MacIntosh): https://opengameart.org/content/metal-impact-sounds
  (thud2, thud3)
- "6 Short Water Splashes" by ezwa, cut by qubodup from public-domain recordings on pdsounds.org:
  https://opengameart.org/content/6-short-water-splashes  (splashes 2 and 4)
- "Deepbassloop80bpm" by deep into perspectives (CC0): https://freesound.org/people/deep%20into%20perspectives/sounds/406809/
  Four bars (12 seconds) cut at the bar attacks and levelled so it loops cleanly: this is "travel".

Synthesized for this mod (MIT, with the mod): the low "whoomph" under the gate opening, the hum under the
idle loop, the whoosh and thump in "teleport", and the falling sweep in "close".

None of these are from any film or TV show.
