Add a `create-protocol` skill

Authoring a conforming protocol currently means reading PROTOCOL_STANDARD.md end to end, and the failure modes are all in the metadata rather than in the science. A skill should do that reading.

It should:

• fill the frontmatter from the standard's current schema, not from a copied example that may have drifted
• ask the two citation questions separately, per ADR 0014 — who published these instructions is protocol_citation and required; who invented the method is method_origin_citation, optional, and omitted rather than guessed at when the protocol originates no method
• write ## Materials and ## Steps with at least one ### Step, since CI rejects a protocol without them
• open ## History & Reviews with a first version entry, a #### Changes list, and *No reviews yet.*
• scaffold the optional parts too, each marked Optional, delete if unneeded. — the ## Notes section, and the optional frontmatter fields: category, tags, upstream_repositories, database_urls, method_origin_citation, artifact_doi, collection_doi. An author who can see a field can decide about it; one who can't discovers it in review, or never
• run scripts/validate-protocol.R before reporting that it's done

The marker has to be literal and uniform, so deleting the unused ones is a search rather than a judgement each time. The same reason the template carries them commented rather than absent.

Lives at skills/create-protocol, beside protocol-runner, on ADR 0007's argument: what a conforming protocol looks like is federation-wide semantics defined by this standard, not something Bioconductor defines.

Worth testing against a summarized-experiment protocol locally before the first PR — writing the skill against the spec alone will miss whatever the spec leaves implicit.

Pairs with #36 (version bumps) and #37 (fixing what the validator reports).

Start with PROTOCOL_STANDARD.md, ADR 0007 and ADR 0014, then inspect the neighboring skills/create-protocol and protocol-runner directories. Use a summarized-experiment protocol as a local example and run scripts/validate-protocol.R. Done means the new skill scaffolds the required and optional sections and fields with the specified marker, and the validator accepts its output.