[Bug]: REST listTasks rejects valid status strings with 500

[hae02y]

What happened?

Is your feature request related to a problem? Please describe.

• GET /tasks?status=working (or input-required, etc.) causes an IllegalArgumentException because the REST handler uses TaskState.valueOf(status). That method only accepts enum names like WORKING, so valid wire strings
  fail and end up as a 500 InternalError.

Describe the solution you'd like

• Parse the status using TaskState.fromString(status) and, on invalid values, return InvalidParamsError (HTTP 422).

Describe alternatives you've considered

• None.

Additional context

• The REST API expects wire strings (working, input-required, etc.) but the handler currently expects enum names. This is why valid requests fail.
• RestHandler.mapErrorToHttpStatus already maps InvalidParamsError to 422, so returning 500 here looks unintended.

Code of Conduct

• I agree to follow this project's Code of Conduct