Fix code scanning alert no. 9: Uncontrolled data used in path expression

[jsommer]

Fixes https://github.com/GitHub-Partner-Demo-Library/MicrosoftCopilotHackathon/security/code-scanning/9

To fix the problem, we need to validate the user-provided path to ensure it does not contain any directory traversal sequences or path separators that could lead to accessing unauthorized files. We will:

1. Normalize the path to remove any redundant elements.
2. Ensure the path is within a specific directory (e.g., a base directory) to prevent access to unauthorized locations.
3. Reject the input if it contains any invalid sequences.

Suggested fixes powered by Copilot Autofix. Review carefully before merging.