Form the Steering Committee and hold first meeting

Give the Steering Committee its target composition in GOVERNANCE.md, then
stand it up and hold its first meeting.

### Acceptance criteria

- Write the Steering Committee charter in GOVERNANCE.md: 5–7 seats, max 2 per organisation, 2-year staggered terms, composition (one rep per subproject + 1–2 elected Community Representatives), and the cap-enforcement mechanism (moved here from #67, which now covers only the subproject/ladder split)
- Each subproject maintainer committee selects its steering representative
- 1–2 Community Representative seats filled by open election
- Initial roster respects the max-2-per-org cap
- First steering meeting held; minutes published (per the restructuring doc's Sep 2026 milestone and the CNCF expectation of published governance minutes)
- Steering committee's ownership scope (vision, governance changes, CNCF interface, subproject add/remove, maintainer election oversight, security response coordination, CoC enforcement ratification, cross-subproject architecture, brand/CNCF resources) confirmed against GOVERNANCE.md
- Coordinate with #68 (org-balanced voting) so the charter and the voting mechanism land together

Start by reading GOVERNANCE.md, then review issues #67 and #68 and the referenced restructuring document to understand the split and voting coordination. Done means the charter and ownership scope are documented, representatives are selected or elected within the organisation cap, and the first meeting minutes are published.

Written by the indexing model from the issue text.