Establish quarterly review cadence and process

[amberb617]

The charter references quarterly reviews but does not define the process.

Proposed process

1. Review window -- two-week period each quarter for community feedback
2. Board review meeting -- board evaluates all feedback and proposed changes
3. Release -- updated framework version published with changelog
4. Retrospective -- board reviews the process itself for improvement

Open questions

• Should quarterly reviews be public or board-only?
• How do we handle breaking changes to the framework?
• What is the minimum notice period before a new version is released?