Fix relative base paths in repository discovery scripts

[GhostwheeI]

Changed the base_path resolution from ../../../ to ../../ in organize_and_readme.py, prefilter_discoveries.py, and validate_organization.py to correctly target the repository root when these scripts are run from the z.repo_support/scripts/ directory.

This fixes permission denied errors that were occurring in the GitHub Actions automation.

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PR created automatically by Jules for task 6900552806864573353 started by @GhostwheeI

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