walltones: quieter, with a steeper falloff

Tuned by ear: nearVolume 1.0 -> 0.8 and farVolume 0.25 -> 0.05. At the old
values a wall out at the full radius was still loud enough to compete with
footsteps and speech, so the tones read as a wash rather than as a cue. The
wider gap between near and far also makes distance easier to judge, which is
the point of the volume ramp.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>

accessibility/walltones.lua

@@ -47,8 +47,8 @@ local config = {
 	sourceRadius = 1.0,
 
 	-- Volume for a wall you are standing next to, and for one out at `radius`.
-	nearVolume = 1.0,
+	nearVolume = 0.8,
-	farVolume = 0.25,
+	farVolume = 0.05,
 
 	-- Set true to invert: a wall further away becomes the louder one.
 	louderWhenFurther = false,