Saturalabs original synthetic notification cues

soft-ping.wav, two-note.wav and low-pulse.wav are original synthetic sine-wave
cues, not recordings of physical instruments or copies of platform alerts.
Saturalabs dedicates these three WAV files under CC0 1.0:
https://creativecommons.org/publicdomain/zero/1.0/
This dedication applies to these three WAVs, not other site media.

Each file is mono, 48 kHz, 16-bit PCM WAV. Durations are 0.48, 0.72 and 0.60
seconds respectively. The first and last samples are zero; measurements.json
contains frame counts, peaks and SHA-256 hashes. These digital checks are not
subjective listening tests or a guarantee of loudness on any device.

To reproduce from the repository root:
python3 scripts/generate-notification-sounds.py