fix: function test query ignores selected stream type (always queries logs) (#13163)

## Problem

Fixes #7228 (新建函数查询时数据流类型无效 — "Data stream type is invalid when creating
a new function query").

In the function editor's **Run query** test panel, selecting **Traces**
(or **Metrics**) as the stream type still queries **logs**. The
user-selected stream type is ignored.

## Root cause

`TestFunction.vue` → `getResults()` hardcoded `page_type: "logs"` when
calling `searchService.search()`:

```js
searchService.search({
  org_identifier: store.state.selectedOrganization.identifier,
  query,
  page_type: "logs",   // ignored the dropdown selection
})
```

`page_type` becomes the `type=` query param in `search.ts`
(`/api/{org}/_search?type=logs&...`), so the request always hit the logs
store regardless of the Stream Type dropdown.

## Fix

Pass the user-selected stream type instead — the same value the rest of
the component already uses for the stream list, field keywords, and
auto-suggest:

```diff
-  page_type: "logs",
+  page_type: selectedStream.value.type,
```

`selectedStream.value.type` is typed `"logs" | "metrics" | "traces"` and
is bound to the Stream Type `OSelect`.

## Blast radius (reviewed)

- **Only consumer of the hardcoded value:** `getResults()` (the "Run
query" button), which fetches sample events into the Events panel to
feed the VRL test. Line 636 was the only hardcoded `page_type`/`"logs"`
in the file — every other reference already uses
`selectedStream.value.type`.
- **Traces:** now correctly reaches the `page_type === "traces"` branch
in `search.ts`, which applies the nanosecond-timestamp response patch
(`patchNsFieldsInJson`) — previously never triggered from this panel.
- **Metrics:** SQL search against metrics streams via
`_search?type=metrics` is valid.
- **Not affected:** the toolbar "Test Function" button (runs the VRL
against the events JSON via the jstransform API — independent of stream
type), saving the function, and the multi-stream `_search_multi` branch
(unused here since `query.query.sql` is always a string).
- **Tests:** `TestFunction.spec.js` / `.spec.ts` mock
`searchService.search` and don't assert `page_type`, so no test changes
are required.

## How to verify

1. **Pipelines → Functions → Add Function** → expand the **Query**
section in the test panel.
2. Set **Stream Type → Traces**, pick a traces stream, enter a query,
click **Run query**.
3. Network tab: the request now goes to `POST
/api/{org}/_search?type=traces...` (was `type=logs`) and returns trace
data.

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-authored-by: Claude Opus 4.8 <noreply@anthropic.com>

web/src/components/functions/TestFunction.vue

@@ -633,7 +633,7 @@ const getResults = async () => {
     .search({
       org_identifier: store.state.selectedOrganization.identifier,
       query,
-      page_type: "logs",
+      page_type: selectedStream.value.type,
     })
     .then((res: any) => {
       expandState.value.stream = false;