DOC Add security release review process

[hannahwestra25]

Description

Adds the customer-facing security links and release governance needed to address the documented partial-compliance gaps:

• links the public security policy from the README, documentation navigation, and CoPyRIT sidebar
• adds a public documentation page covering private vulnerability reporting and release security notices
• requires the release owner to review customer-facing release materials and record evidence in a release work item
• requires a different PyRIT maintainer to review and approve the final materials before publishing
• defines required security and compatibility content for every release's notes, including explicit "none known" statements
• keeps details about security vulnerabilities that have not yet been publicly disclosed in the existing private reporting process

Tests and Documentation

• npm test -- --runInBand src/components/Sidebar/Navigation.test.tsx
• npm run type-check
• npx eslint src/components/Sidebar/Navigation.tsx src/components/Sidebar/Navigation.test.tsx --max-warnings 0
• jupyter-book build --html

[romanlutz]

Can we start with this post-v1?