docs(api): /analytics/query 的 fields[] 只有 name / type，删掉示例里的 label / format 并写明两层的分工 (#6369) (#6441)

`POST /analytics/query` 的响应示例给 `data.fields[]` 三个条目都标了 `label`、
中间那个还标了 `format`，而这个端点的任何一条产出路径都只发 `{ name, type }`。
照文档写的客户端读 `fields[i].label` 渲染表头、读 `format` 格式化金额，拿到的
是 `undefined` —— 不像拼写错误那样当场 400，而是安静地渲染出空表头。

删掉这四个键，并补一段 Callout 说明两层的分工：display name 与 format 是
cube 的 metric/dimension **定义**的属性（`MetricSchema.label` / `.format`），
从 cube 元数据读，不在查询结果里。只删键不解释，下一个读者会重新推导出同样的
错误期待。


Claude-Session: https://claude.ai/code/session_01BDmDsu2575gDxeMCxXhDE3

Co-authored-by: Claude <noreply@anthropic.com>

Author: hotlong

content/docs/api/data-api.mdx

@@ -371,15 +371,28 @@ Filtering uses the canonical Query DSL `where` object (the same MongoDB-style `F
       { "industry": "Healthcare", "revenue_sum": 80000, "count": 3 }
     ],
     "fields": [
-      { "name": "industry", "type": "string", "label": "Industry" },
-      { "name": "revenue_sum", "type": "number", "label": "Revenue Sum", "format": "$0,0" },
-      { "name": "count", "type": "number", "label": "Count" }
+      { "name": "industry", "type": "string" },
+      { "name": "revenue_sum", "type": "number" },
+      { "name": "count", "type": "number" }
     ],
     "sql": "SELECT ..."
   }
 }
 ```
 
+<Callout type="info">
+**`fields[]` describes columns, not presentation.** Each entry carries exactly `name` and
+`type` — that is the whole descriptor `AnalyticsResultResponseSchema` declares, and every
+strategy answering this endpoint emits those two keys and nothing else.
+
+Display name and number format live one layer up, in the **cube's metric/dimension
+definition** (`MetricSchema.label` / `MetricSchema.format`, `DimensionSchema.label`), and
+are read from cube metadata — `GET /analytics/meta` below reports each measure's and
+dimension's declared label as `title`. Reading `data.fields[i].label` or
+`data.fields[i].format` off a query result yields `undefined`; a client that renders table
+headers or formats amounts reads them from the cube metadata instead.
+</Callout>
+
 ### `GET /analytics/meta`
 
 Get metadata for all registered cubes. Cubes are explicitly defined (via `defineCube`