[Good first issue]: Add rel="noopener noreferrer" to external links

[FrankezeCode]

Summary

External links that open in a new tab should include rel="noopener noreferrer" for security. Audit and fix any missing instances.

What should change?

• Search for target="_blank" across src/
• Add rel="noopener noreferrer" where missing
• Priority files: check-in success explorer links, passport explorer links

Acceptance criteria

All target="_blank" links have proper rel
No broken links
Build passes
Checklist of done conditions:

• Audit completed (list files changed in PR)
• Every external _blank link fixed
• npm run build passes
• No unrelated link changes

How to test

1. Grep repo for target="_blank" after changes
2. Click fixed links (e.g. block explorer after check-in)
3. Confirm they open in new tab correctly

[lucasvass1]

I'm going to work on it.