fix(deploy): k8s backend 注入 AI 相关环境变量

生产环境 deployment 缺 AI_ENABLED/AI_API_KEY 等变量，导致 scheduler
里的 AI OKR 分析分支被跳过，cron 只跑了 gitea 同步而没触发 OKR 更新。

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

k8s/backend-deployment.yaml

@@ -48,6 +48,15 @@ spec:
         # CORS
         - name: CORS_ORIGINS
           value: "https://devperf.airlabs.art"
+        # AI (豆包 Doubao / 火山引擎 Ark)
+        - name: AI_ENABLED
+          value: "true"
+        - name: AI_API_KEY
+          value: "846b6981-9954-4c58-bb39-63079393bdb8"
+        - name: AI_MODEL
+          value: "doubao-seed-2-0-pro-260215"
+        - name: AI_BASE_URL
+          value: "https://ark.cn-beijing.volces.com/api/v3"
         livenessProbe:
           httpGet:
             path: /api/health