assets+docs: rename the master recording to "The Falls"

Drop the working-title version suffix: The_Falls_v3.1.{mp3,ogg,wav} ->
The_Falls.{mp3,ogg,wav}, and update the architecture brief reference. This is the
source master in assets/; the runtime loop files (waterfall.ogg / waterfall.m4a)
are unchanged.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

Author: JacobStephens2

assets/The_Falls_v3.1.mp3 assets/The_Falls.mp3assets/The_Falls_v3.1.mp3 renamed to assets/The_Falls.mp3

@@ -1802,4 +1802,4 @@ If you want me to pick for you based on your stated goal (“a simple tool I’l
 
 The clave-tech-stack.md file is at docs/clave-tech-stack.md.
 
-The audio files are in the assets folder. The_Falls_v3 is available in three formats: MP3, OGG, and WAV there.
+The audio files are in the assets folder. The_Falls is available in three formats: MP3, OGG, and WAV there.