Rename Claude sandbox to Assistant and update docs/volumes

sandbox/docker-compose.yml

@@ -1,5 +1,5 @@
 services:
-  claude:
+  assistant:
     image: sandbox
     env_file:
       - path: ./.env
@@ -10,7 +10,7 @@ services:
     volumes:
       - .:/workspace                          # default; overridden by claude.py at runtime
       - claude_target:/workspace/target       # persist Rust build cache
-      - claude_userhome:/home/claude          # persist Claude settings, auth, history
+      - assistant_userhome:/home/claude          # persist Claude settings, auth, history
       - ./.container-abra:/home/claude/.abra  # default; overridden by claude.py at runtime
       - tailscale_state:/var/lib/tailscale    # persist Tailscale auth across restarts
     tty: true
@@ -18,5 +18,5 @@ services:
 
 volumes:
   claude_target:
-  claude_userhome:
+  assistant_userhome:
   tailscale_state: