Adds the ding sound effect that fires on speed-limit changes / cruise-
warning transitions (writers will set ClearpilotPlayDing="1" in
/dev/shm/params; soundd polls at ~2Hz, clears the flag, plays once).
The ding plays at MAX_VOLUME independent of the alert volume map and
mixes into the same output stream. Single-shot — no looping. Loaded
once at startup; failure to load just disables the ding (rest of soundd
keeps working).
print-to-stderr, not cloudlog (CLAUDE.md rule).
brianhansonxyz
5d2fe5248b