fix: add checks to avoid cloning existing repositories on rebuilds

[FidelusAleksander]

Summary

When rebuilding container in an existing codespace there were gh cli errors raised when trying to clone an existing repo

Changes

Closes:

Task list

• For workflow changes, I have verified the Actions workflows function as expected.
• For content changes, I have reviewed the style guide.

[Copilot]

Pull Request Overview

This PR fixes an issue where the postCreate.sh script would fail when rebuilding containers in an existing codespace due to attempting to clone repositories that already exist.

• Added directory existence checks before cloning repositories
• Replaced direct GitHub URLs with shorthand repository names
• Added informative echo statements during cloning operations

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