Document HeartMuLa test routing and timing

experiments/heartmula-3b/README.md

@@ -39,7 +39,10 @@ docker compose up -d heartmula-test
 docker compose logs -f heartmula-test
 ```
 
-The temporary test UI is then available on port `7863`. Stop it with:
+The temporary test UI listens locally on port `7863`. During the listening
+test it is proxied through Athena's existing WireGuard gateway; permanent
+dashboard/gateway integration is deliberately deferred until the audio has
+been accepted. Stop it with:
 
 ```sh
 docker compose down

experiments/heartmula-3b/compose.yaml

@@ -16,7 +16,9 @@ services:
       - /data/models/heartmula:/models:ro
       - /data/music/heartmula:/output
     ports:
-      - "7863:7860"
+      - "127.0.0.1:7863:7860"
+    networks:
+      - frontend
     deploy:
       resources:
         reservations:
@@ -30,3 +32,8 @@ services:
       timeout: 5s
       retries: 20
       start_period: 180s
+
+networks:
+  frontend:
+    external: true
+    name: mike-ai_frontend