feat(k8s): 实时日志流 + WebSocket exec 交互终端 + 前端流式日志查看器

后端:
  - GetPodLogsStream: 新增 K8s follow=true 流式日志读取
  - GetPodLogs handler: 支持 stream=true → chunked transfer 实时推流
  - ExecTerminal: WebSocket → K8s SPDY exec 双向代理 (交互式 bash)
  - 路由: GET /ws/k8s-exec/:id/namespaces/:ns/pods/:pod (WebSocket)

前端 DeploymentDetail:
  - 新增「实时流」按钮: fetch ReadableStream + TextDecoder 逐块渲染
  - 日志内容自动滚动追加

CD/CI 镜像更新:
  - POST /update-image 已可用 (前端表单+后端 API 均完成)

backend/pkg/k8sclient/client.go

@@ -467,6 +467,25 @@ func (c *Client) GetPodLogs(namespace, podName, container string, tailLines int)
 	return string(body), nil
 }
 
+// GetPodLogsStream returns the raw streaming response body for follow=true
+func (c *Client) GetPodLogsStream(namespace, podName, container string, tailLines int) (io.ReadCloser, error) {
+	path := fmt.Sprintf("/api/v1/namespaces/%s/pods/%s/log?follow=true&tailLines=%d", namespace, podName, tailLines)
+	if container != "" {
+		path += "&container=" + container
+	}
+	url := c.BaseURL + path
+	resp, err := c.HTTPClient.Get(url)
+	if err != nil {
+		return nil, fmt.Errorf("GET logs stream: %w", err)
+	}
+	if resp.StatusCode >= 400 {
+		body, _ := io.ReadAll(resp.Body)
+		resp.Body.Close()
+		return nil, fmt.Errorf("K8s API %d: %s", resp.StatusCode, string(body[:min(len(body), 300)]))
+	}
+	return resp.Body, nil
+}
+
 // --- Scale ---
 
 // ScaleDeployment patches the replicas count for a deployment