fix: use container IP instead of port mapping for health check

When running inside Gitea Actions runner (Docker-in-Docker),
127.0.0.1:HOST_PORT doesn't work because the runner container
doesn't have access to the host's port mappings.
Use docker inspect to get the container's direct IP address.

tests/test.sh

@@ -39,10 +39,10 @@ assert_match() {
 echo "Running container: $IMAGE"
 docker run -d --name "$CONTAINER_NAME" -p 0:8080 "$IMAGE" >/dev/null
 
-HOST_PORT=$(docker port "$CONTAINER_NAME" 8080/tcp | head -1 | cut -d: -f2)
-BASE_URL="http://127.0.0.1:${HOST_PORT}"
+CONTAINER_IP=$(docker inspect -f '{{range .NetworkSettings.Networks}}{{.IPAddress}}{{end}}' "$CONTAINER_NAME")
+BASE_URL="http://${CONTAINER_IP}:8080"
 
-echo "Waiting for container (port $HOST_PORT)..."
+echo "Waiting for container (ip $CONTAINER_IP)..."
 for i in $(seq 1 30); do
   if curl -sf "$BASE_URL/" >/dev/null 2>&1; then
     echo "Container ready after ${i}s"