helpers.md: tool runner method heading is missing the .beta segment

Thanks for the tool runner helpers, they are handy.

While reading helpers.md I noticed the method reference heading drops the `beta` segment, so the path as written does not resolve on the client.

helpers.md line 359:

```
### `client.messages.toolRunner(params): BetaToolRunner`
```

`toolRunner` is only defined on the beta Messages resource (`src/resources/beta/messages/messages.ts`). The non-beta `src/resources/messages/messages.ts` exposes `create`, `parse`, `stream`, and `countTokens`, but no `toolRunner`. Every runnable example in the same file calls `anthropic.beta.messages.toolRunner(...)` (lines 199, 215, 237, 266), so the heading looks like a dropped `.beta`.

Suggested fix:

```
### `client.beta.messages.toolRunner(params): BetaToolRunner`
```

I checked the open docs PR #881 and this particular heading looks untouched by it, so flagging separately. Happy to open a PR instead if you prefer.

Open helpers.md around line 359 and compare the method heading with src/resources/beta/messages/messages.ts and src/resources/messages/messages.ts. Check the runnable examples at lines 199, 215, 237, and 266, then confirm the reference heading uses the same beta path as those examples; the documentation is done when the heading resolves to the beta tool runner.

Escrita pelo modelo de indexação a partir do texto da issue.