CCM-18514: Gitleaks Config Improvements

[jamesthompson26-nhs]

Description

Updated the secret-scanning hook to provide clearer, actionable guidance when a secret finding is detected, while preserving normal gitleaks behavior and keeping CI execution predictable.

• Added explicit remediation guidance when findings are detected, including a direct link to the PLAT-KOP-020 false-positive handling guidance.
• Made the failure message more visible with prominent alert styling and terminal color formatting (with safe plain-text fallback when color is unavailable).
• Scoped the custom guidance so it appears for findings only, not for unrelated runtime/tooling failures.
• Added CI-safe behavior so pseudo-terminal handling is disabled when running in CI, ensuring deterministic pipeline behavior.

Context

Secret scan failures were not giving contributors a consistent and clear, immediate path to resolve or safely handle false positives. This change improves developer experience by surfacing obvious next steps directly in the failure output, reducing confusion and rework during commit and pre-commit checks.

At the same time, the implementation avoids regressions by:

• Keeping gitleaks output readable and familiar in local interactive runs.
• Preventing local terminal behavior from causing unpredictable CI outcomes.
• Ensuring the enhanced messaging does not mask non-finding operational errors.

Type of changes

• Refactoring (non-breaking change)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would change existing functionality)
• Bug fix (non-breaking change which fixes an issue)

Checklist

• I am familiar with the contributing guidelines
• I have followed the code style of the project
• I have added tests to cover my changes
• I have updated the documentation accordingly
• This PR is a result of pair or mob programming

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• I confirm that neither PII/PID nor sensitive data are included in this PR and the codebase changes.