HUMAN task: missing builder class

## Summary

`TaskType.HUMAN` exists in the SDK enum but there is no `Human` builder class in
`conductor-client/…/def/tasks/`. Users cannot create a HUMAN task using the fluent SDK API.

## Server baseline

Conductor **3.32.0-rc.9**

## Evidence

**Static:** `TaskType.HUMAN` is in the enum; no `Human.java` file under
`conductor-client/…/def/tasks/`.

**Live (2026-07-16):** A raw `WorkflowTask` with `"type": "HUMAN"` was registered
and executed against Conductor OSS 3.32.0-rc.9. The workflow entered RUNNING state
awaiting human signal (expected behavior) — server accepts HUMAN tasks, gap is SDK-only.

## Expected behaviour

```java
new Human("human_approval_ref")
```

## Proposed fix

```java
public class Human extends Task {
public Human(String taskReferenceName) {
super(taskReferenceName, TaskType.HUMAN);
}
}
```

No `updateWorkflowTask` override required — HUMAN has no required `inputParameters`.

## Related

Discovered during systematic SDK audit against Conductor OSS 3.32.0-rc.9.

Start in conductor-client/…/def/tasks/ and compare the existing builder classes with the TaskType enum entry for HUMAN. Add the missing Human builder so new Human("human_approval_ref") can be created through the fluent SDK API; done means it represents a HUMAN task without requiring input parameters.

Written by the indexing model from the issue text.