Share the Ready issue search between the Pickup run and the Architect run #324

Parent

#311

What to build

A prefactor that changes no behaviour. The Pickup run's search for the lowest-numbered Ready issue in a repository (Unready labels, Claim, Ticket inside a Spec, Base fix issue, open blockers, started, Spec whose Tickets are all closed, settle time) becomes one function that any run can call, so that an Architect run can later ask "does this repository have a Ready issue?" against the very same definition. The Sweep and the Claim limit stay in the Pickup run: they belong to it, not to the search.

Acceptance criteria

• The Ready issue search can be called from outside the Pickup run and returns the lowest-numbered Ready issue, if any, with whether it is a Spec.
• The Pickup run uses that function. Its progress lines, its "why each issue was passed over" lines and its gh calls are unchanged, in the same order.
• The existing Pickup run suite passes unchanged. cargo test, cargo clippy --all-targets -- -D warnings and cargo fmt --check pass.

Blocked by

None (can start immediately)