Summary of PR

This PR updates openhands/agenthub/README.md so its task-management documentation matches the current implementation.

Specifically, it:

• replaces the stale AddTaskAction / ModifyTaskAction references with TaskTrackingAction
• fixes the broken ../events/action/tasks.py links by pointing readers to the current action definition
• adds TaskTrackingObservation to the observations list so the documented action/observation surface stays in sync

Demo Screenshots/Videos

N/A

Change Type

• Bug fix
• New feature
• Breaking change
• Refactor
• Other (dependency update, docs, typo fixes, etc.)

Checklist

• I have read and reviewed the code and I understand what the code is doing.
• I have tested the code to the best of my ability and ensured it works as expected.

Fixes

Resolves #(issue)

Release Notes

• Include this change in the Release Notes.