Remove public contact email

[BennettKnight]

What changed

• Removed the personal email address from the code of conduct and security policy.
• Directed security reports to GitHub private vulnerability reporting.
• Directed conduct reporters to request private maintainer follow-up without posting sensitive details.

Validation

• Confirmed the current tracked files contain no hellogumbo.com email address or mailto link.
• Confirmed the diff contains only CODE_OF_CONDUCT.md and SECURITY.md.