docs: name pull request 4 as the subject to land

[juliantellez]

What. Adds docs/subject-4-the-oldest-with-a-red-check.md. The file names the pull request to
land, with its number, title, head branch, head commit, conflict state and the name of every check
that is not passing.

Why. The next step runs in a new session. It reads nothing from this one, so the pick has to be
written down.

The subject is pull request 4, #4. It is the oldest
of the thirteen open pull requests. It is the only one with a check that is not passing. That check
is plan and apply, and its conclusion is failure.

gh pr checks 4 does not print that check. It prints two passes and exits 0. The deploy workflow
starts on a push to main and on a manual start, never on a pull request, so GitHub keeps the run
out of the pull request summary. Read the check runs on the head commit instead. An absent check
looks the same as a passing check.

I checked the exclusions. No open pull request is a draft. Every base branch is main, so no head
branch carries a child. I did not trust the MERGEABLE label for the conflict test: I ran
git merge-tree --write-tree origin/main <head> on all thirteen heads, and each one exits 0 with no
conflict line.

Gates on this branch, each run as its own command: npm ci, npm run typecheck, npm run lint,
npm run test:count (75 total, 75 passed, 0 failed), npm run build, npm run verify:package
(GET / answered 200 with 4697 bytes), terraform fmt -check -recursive, terraform init -backend=false and terraform validate. Every one exits 0.