Add an overlay soundboard and fix playback command bugs.

Stop was advancing the queue, history overwrote the day file, and slash commands often never replied; soundboard clips now mix on top of the current track.

Co-authored-by: Cursor <cursoragent@cursor.com>

docker-compose.yml

@@ -7,6 +7,7 @@ services:
     restart: always
     volumes:
       - ./data:/app/data
+      - ./history:/app/history
     env_file:
       - .env
     environment: