NOOP task type: missing from TaskType enum and no builder function

## Summary

`TaskType.NOOP` is absent from the `TaskType` enum in `src/open-api/types.ts`. There
is no `noopTask()` builder function. Users cannot create a NOOP workflow task using
the SDK.

`NOOP` does appear as a string literal in the generated `types.gen.ts`
(`workflowTaskType` union) but is not promoted to the `TaskType` enum.

## Server baseline

Conductor **3.32.0-rc.9**

## Evidence

**Static:** `TaskType` enum in `types.ts` ends at `LIST_MCP_TOOLS`; no `NOOP` entry.

**Live (2026-07-16):** A raw task with `"type": "NOOP"` was registered and executed
against Conductor OSS 3.32.0-rc.9. The workflow completed successfully — server supports NOOP
fully, the gap is SDK-only.

## Proposed fix

Add to `TaskType` enum in `src/open-api/types.ts`:
```typescript
NOOP = "NOOP",
```

Add builder `src/sdk/builders/tasks/noop.ts`:
```typescript
import type { WorkflowTask } from "../../../open-api";
import { TaskType } from "../../../open-api";

export const noopTask = (
taskReferenceName: string,
optional?: boolean
): WorkflowTask => ({
name: taskReferenceName,
taskReferenceName,
type: TaskType.NOOP,
inputParameters: {},
optional,
});
```

Export from `builders/tasks/index.ts`.

## Related

Discovered during systematic SDK audit against Conductor OSS 3.32.0-rc.9.
Same gap in Java SDK (conductor-oss/java-sdk#130) and Python SDK (conductor-oss/python-sdk#430).

从 src/open-api/types.ts 中的 TaskType 枚举开始，然后检查 src/sdk/builders/tasks/index.ts 中的任务构建器和导出项。在 src/sdk/builders/tasks/noop.ts 中添加 NOOP 构建器并将其导出，以便用户可以使用 TaskType.NOOP 创建 WorkflowTask。

由索引模型根据 Issue 内容生成。