fix(deploy-mining): ensure_kafka_image 输出到 stderr 避免被 $() 捕获

docker pull 在 group_info=$(run_kafka_cmd ...) 内执行时，stdout 被命令替换
捕获到变量中，屏幕无任何输出导致脚本看起来卡住。
- ensure_kafka_image 输出重定向到 stderr
- full_reset 开头显式预拉取镜像

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

backend/services/deploy-mining.sh

@@ -333,8 +333,9 @@ run_psql() {
 ensure_kafka_image() {
     local image="confluentinc/cp-kafka:7.5.0"
     if ! docker image inspect "$image" &>/dev/null; then
-        log_info "Pulling Kafka CLI image: $image (first time only)..."
-        docker pull "$image"
+        # Output to stderr so it's visible even when called inside $(...) command substitution
+        echo -e "${BLUE}[INFO]${NC} Pulling Kafka CLI image: $image (first time only)..." >&2
+        docker pull "$image" >&2
     fi
 }
 
@@ -1277,6 +1278,9 @@ full_reset() {
         docker compose $COMPOSE_ARGS up -d postgres-2 redis-2 2>/dev/null || true
         docker compose $COMPOSE_ARGS up -d --wait postgres-2 redis-2 2>/dev/null || sleep 15
         log_success "Standalone infrastructure is up"
+
+        # Pre-pull Kafka CLI image (needed for cross-server kafka commands)
+        ensure_kafka_image
     fi
 
     log_step "Step 1/19: Stopping 2.0 services..."