fix: Address Snyk SAST findings

[mfish911]

Summary

My company uses Snyk SAST as part of security reviews and came back with a list of findings including path traversal, SSRF, XSS and ReDoS potential issues. This pull request addresses all the findings.

Change Type

Please delete any irrelevant options.

• Bug fix (non-breaking change which fixes an issue)

Testing

Validated that core functionality continues to work with these updates.

Test Configuration:

Checklist

Please delete any irrelevant options.

• I have performed a self-review of my own code

[danny-avila]

Check the eslint warnings

[github-actions]

👋 Thanks for the contribution! LibreChat merges all changes into dev first — main only moves at release time — so this pull request's base branch was switched from main to dev automatically.

Nothing is needed from you; your commits, reviews and discussion are unchanged. If the diff now shows files you did not touch, rebase onto dev:

git remote add upstream https://github.com/LibreChat-AI/LibreChat.git
git fetch upstream dev
git rebase upstream/dev
git push --force-with-lease

Maintainers: apply the target: main label and restore the base branch if this one genuinely belongs on main.