fix: Remove NATS healthcheck — use service_started instead

NATS minimal image has no shell tools for health probes. The API
already handles NATS unavailability gracefully, so service_started
is sufficient.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

docker/docker-compose.yml

@@ -28,12 +28,6 @@ services:
       - ./nats.conf:/etc/nats/nats.conf:ro
     ports:
       - "8089:4222"   # Client connections
-    healthcheck:
-      test: ["CMD-SHELL", "echo > /dev/tcp/localhost/4222 || exit 1"]
-      interval: 5s
-      timeout: 3s
-      retries: 5
-      start_period: 5s
 
   api:
     build:
@@ -62,7 +56,7 @@ services:
       postgres:
         condition: service_healthy
       nats:
-        condition: service_healthy
+        condition: service_started
     ports:
       - "8088:3000"