adjust CliAgentEnv sandbox creation timeout + remove DummyHarborEnv

[kcoopermiller]

Description

Type of Change

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to not work as expected)
• Documentation update
• Test improvement

Testing

• All existing tests pass when running uv run pytest locally.
• New tests have been added to cover the changes

Checklist

• My code follows the style guidelines of this project as outlined in AGENTS.md
• I have performed a self-review of my own code
• I have commented my code, particularly in hard-to-understand areas
• I have made corresponding changes to the documentation
• My changes generate no new warnings
• Any dependent changes have been merged and published

Additional Notes

---

Note

Low Risk
Low risk: removes an example environment and tweaks sandbox creation polling; main behavioral change is potentially longer waits during sandbox startup if the service is slow or hung.

Overview
Removes the dummy_harbor_env example Harbor/CliAgent sandbox environment (code, packaged metadata, and bundled hello-world task), and updates environments/README.md to stop referencing it.

Adjusts CliAgentEnv sandbox startup to wait longer for creation by passing max_attempts=120 to wait_for_creation, increasing tolerance for slower sandbox provisioning.

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