Formalise non-EDB maintainer pathway

Document and execute the promotion path from contributor → subproject maintainer, and elevate initial non-EDB candidates named in the restructuring proposal.

### Acceptance criteria

- Contributor ladder / promotion criteria documented (org-member definition, review cadence — "monthly review of contributors for advancement" per subproject committees)
- Initial non-EDB subproject maintainers formalised, starting with those already named as component owners
- Each formalised maintainer is CNCF-recognised with a governance voice via their subproject's steering representative
- Satisfies the graduation-stage 2-organisation maintainer requirement ahead of time, per the proposal's recommendation to formalise now rather than defer

Start by locating the restructuring proposal referenced in the issue and extract its named component owners, contributor ladder, and steering-representative details. Document the promotion criteria and monthly review cadence, then formalise the identified non-EDB maintainers and verify that each has a governance voice and supports the two-organisation maintainer requirement.

Written by the indexing model from the issue text.