feat(aidd-pm): refinement skill — dedup, split, estimate, criteria #147

Add a refinement skill to aidd-pm: an activity verb applied to a backlog that already exists. Absorbs the Three Amigos ritual of #352, which is a method, not a domain.

Why these live here

Per R2 of the skill-authoring contract, a skill is a domain, not a method. Deduping, splitting, estimating, writing missing acceptance criteria and running a Three Amigos pass are all things one does to a backlog. They are actions of one skill, and none of them produces an artifact of its own.

Actions

• dedup — find issues that describe the same work; propose the survivor.
• split — break an issue too large to estimate into vertical slices.
• estimate — size what carries no estimate.
• acceptance-criteria — write the criteria missing from an issue (ex-feat(aidd-pm): acceptance criteria + spikes skill #355).
• three-amigos — one pass over a story through the PM, dev and QA lens (ex-feat(aidd-pm): Three Amigos refinement skill #352).

Acceptance criteria

• Runs against a GitHub issue backlog and against a markdown backlog.
• Never closes or edits an issue without stating the reason.
• Each action is independently invocable.
• When an issue cannot be estimated, grooming names the unknown and points at aidd-pm:spike (feat(aidd-pm): spike skill — a timeboxed question with a written answer #412); it does not run the spike itself.

Out of scope

• Spikes — extracted to feat(aidd-pm): spike skill — a timeboxed question with a written answer #412: a spike produces a document, refinement operates on a backlog.
• Brownfield product audit — analysing an existing product, not its backlog, was bundled into this issue's original scope. Different domain, needs its own issue when the need is real.