docs(agents): configure engineering skill contracts

[pablontiv]

What

Configure the repository contracts consumed by Matt Pocock's engineering skills:

• declare GitHub Issues as the tracker
• map the canonical triage state labels
• document the single-context domain documentation layout
• add the corresponding Agent skills pointers to CLAUDE.md

Related issue

Deliberately unlinked: this repository setup was requested directly and has no tracking issue.

Why

Skills such as triage, to-spec, to-tickets, and wayfinder need an explicit tracker, label vocabulary, and domain-documentation layout instead of inferring repository conventions.

How

Added the canonical configuration documents under docs/agents/ and linked them from CLAUDE.md. Pull requests remain excluded from automatic triage discovery by default. The referenced GitHub triage and wayfinder labels were provisioned separately in the repository.

Checklist

• Tests pass (go test ./... -race)
• Code is clean (go vet ./...)
• Changes are documented if user-facing
• Deliberately left unlinked because no issue exists