Meet CZI open-source repo requirements #474

Just some things to add from the CZI Confluence Wiki.

Required (MUST)

• Add SECURITY.md — report contact security@chanzuckerberg.com
• README.md: add Code of Conduct section (Contributor Covenant) + Reporting Security Issues section linking SECURITY.md
• Enable GitHub Advanced Security on mehta-lab/VisCy and clear findings (repo admin)
• Confirm/enable branch protection on main — no classic protection found; check rulesets (repo admin)

Should (to exceed)

• Add CODE_OF_CONDUCT.md (Contributor Covenant v2.1) — decide enforcement contact for the [INSERT CONTACT METHOD] placeholder
• Add .github/ISSUE_TEMPLATE/ (bug_report.md, feature_request.md, config.yml)
• Add .github/PULL_REQUEST_TEMPLATE.md
• CONTRIBUTING.md: add security-reporting line linking SECURITY.md
• README.md: add a project-status statement ("under active development")