fix: align CDCF role description with bylaws and manifesto

[JohnRDOrazio]

Summary

• The section "The CDCF Role: Validation Standards, Not Data Commons" in the trusted synthetic data memo explicitly denied the CDCF a data commons role, contradicting the bylaws (which charge the Foundation to steward "data repositories") and the manifesto (which describes a "builder commons")
• Renamed the section to "Federated Data Commons and Validation Standards" and revised the body to frame the CDCF as both a standards body and a federated data commons, with a phased approach
• Added a fourth contribution — Shared data repository stewardship — to the role table, aligning with the bylaws' data repository language

Test plan

• Verify internal TOC anchor link resolves correctly
• Review revised section for consistency with bylaws at https://catholicdigitalcommons.org/about/bylaws and manifesto at https://catholicdigitalcommons.org/about/manifesto
• Confirm no broken cross-references to the old heading in other documents

🤖 Generated with Claude Code

[JohnRDOrazio]

Superseded by #9, which incorporates the changes from this PR (bylaws/manifesto grounding, data commons reframing) within a more comprehensive restructuring:

• AI Governance folded into unified Project Vetting Criteria (v0.2)
• All three research memos generalized beyond AI-only scope
• Three-tier data model (sensitive → local → universal Church data) with copyright-aware hybrid hosting for local adaptations
• CDCF role grounded in bylaws and manifesto charter language

Closing in favor of #9.