fix: 后端健康检查改用TCP探针，修复CrashLoopBackOff

后端没有/api/health/路由，HTTP探针返回404导致Pod被反复重启，
改用tcpSocket探针检测8000端口即可。

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

k8s/backend-deployment-prod.yaml

@@ -41,24 +41,16 @@ spec:
         - name: CORS_ORIGINS
           value: "https://airlabs-manage-web.airlabs.art"
         livenessProbe:
-          httpGet:
+          tcpSocket:
-            path: /api/health/
             port: 8000
-            httpHeaders:
-            - name: Host
-              value: localhost
           initialDelaySeconds: 30
           periodSeconds: 10
-          timeoutSeconds: 5
+          timeoutSeconds: 3
           failureThreshold: 3
         readinessProbe:
-          httpGet:
+          tcpSocket:
-            path: /api/health/
             port: 8000
-            httpHeaders:
+          initialDelaySeconds: 10
-            - name: Host
-              value: localhost
-          initialDelaySeconds: 15
           periodSeconds: 5
           timeoutSeconds: 3
           failureThreshold: 3