docs: name pull request 4 as the subject to land

[juliantellez]

What. Records which open pull request is next to land, in subject.md. The next step is a new
session that reads nothing from this one, so the file carries the number, the title, the head
branch, the head commit, the conflict state and the failing check.

Why. Pull request 4 is the older of the two open ones. It does not conflict, and one check on
its head commit failed: plan and apply.

That check does not appear in gh pr checks 4, which prints code and infrastructure, says both
pass, and exits 0. The deploy workflow runs on a push to main and on a manual start, never on a
pull request, so GitHub keeps its run out of the pull request summary. Reading the head commit
shows it:

gh api repos/atlantic-blue/transcript/commits/84d9fe37/check-runs --jq '.check_runs[] | .name'

Two things the file records that a reader needs. Every deploy run in the repository failed, on
main as well as on that branch, so pull request 4 does not cause the red check. And main has no
branch protection, so no check is required and none blocks a merge.

Pull request 5 is an earlier round of this same task and names the same subject. It is still open.
Both add subject.md at the root, so whichever merges second will conflict.