feat(android): extract structured purchase requirements

docs/api.md

@@ -292,13 +292,29 @@ App 空闲或运行时上报设备状态；运行时任务续租使用任务专
     {"name": "color", "value": "black", "source": "text"},
     {"name": "capacity", "value": "about 20L", "source": "text"}
   ],
+  "sku": "BLACK-20L",
   "quantity": 2,
   "max_budget": "200.00",
   "confidence": 0.86,
-  "warnings": []
+  "warnings": [],
+  "manual_review": {
+    "required": false,
+    "reasons": []
+  },
+  "provenance": {
+    "provider_id": "configured-provider",
+    "model": "configured-model",
+    "prompt_version": "requirement-extraction-v1",
+    "reference_image_sha256": "64-char-lowercase-hex"
+  }
 }
 ```
 
+`sku`、`quantity` 和 `max_budget` 必须来自原始任务，不能采用模型返回值。第一层
+`ProbeTask` 尚无预算字段，因此 T-103 输出 `max_budget: null` 并追加
+`MAX_BUDGET_NOT_PROVIDED` 警告。属性 `source` 的 API 表示使用小写
+`title/image/both`；供应商响应在 adapter 内规范化后才进入此合约。
+
 ### `POST /api/v1/tasks/{task_id}/ai/evaluate-candidate`
 
 ```json