Skill: update-conventions

Edits to docs/CONVENTIONS.md and docs/CHARTER.md are not normal PRs — they change how everyone works in the repo. They go through RFC review.

Procedure

1. Push back if the user starts editing directly. Conventions changes are high-leverage; they should be deliberated.

2. Open an RFC instead. Use the new-rfc skill, with the RFC scoped to "change conventions section X to Y". The RFC's Proposal section should contain the specific edited text — the diff, essentially.

3. After the RFC is accepted, the actual edit to CONVENTIONS.md is a small PR that cites the RFC in the commit footer:

   docs(conventions): adopt RFC-NNNN — <one-line summary>
   
   Implements RFC-NNNN: <link>
   

4. Update the RFC's Follow-on artifacts section to point at the merged commit.

Exception

Trivial edits — typo fixes, broken-link fixes, formatting — don't need an RFC. A normal PR is fine. If you're not sure, err toward RFC: the cost of an extra RFC is small; the cost of an unannounced rule change is large.