refactor: drop the reviewer rotation and rely on CODEOWNERS

CONTRIBUTING.md

@@ -36,18 +36,16 @@ You are on the [DNS Managers
 team](https://github.com/orgs/WITCodingClub/teams/dns-managers). A pull request
 cannot merge without an approving review from one of you.
 
-### Reviews go round the team
+### Reviews go to the whole team
 
-A workflow asks one person per pull request, in rotation. The rotation is
-[`.github/dns-reviewers.txt`](./.github/dns-reviewers.txt). It skips the author
-of the pull request.
+`CODEOWNERS` makes the team a required reviewer, so GitHub asks all of you on
+every pull request. Whoever gets to it first reviews it.
 
-Being asked does not make it only your job. Anybody on the team can approve.
-If you cannot get to a review, say so on the pull request so that somebody else
-picks it up.
+Nobody is assigned. That means a pull request can sit while each of you assumes
+the other has it. If you start a review, say so on the pull request, and if you
+cannot get to one, say that too.
 
-To change the rotation, edit the file and open a pull request. Comment out a
-line to pause somebody. Add a line to bring somebody in.
+To change who reviews, change who is on the team.
 
 ### What to check in a review
 

README.md

@@ -56,13 +56,11 @@ in this order by itself.
 
 ### 2. Open a pull request
 
-A bot adds two things to your pull request:
+A bot posts a **plan** on your pull request. It lists every record the merge
+would create, change, or delete. Read it. If it shows something you did not
+intend, fix your branch.
 
-- **A plan.** It lists every record the merge would create, change, or delete.
-  Read it. If it shows something you did not intend, fix your branch.
-- **A reviewer.** The rotation in
-  [`.github/dns-reviewers.txt`](./.github/dns-reviewers.txt) decides whose turn
-  it is.
+The DNS Managers team is asked to review automatically.
 
 Push more commits to the same branch if the reviewer asks for changes. Do not
 close the pull request and open a new one.

docs/runbook.md

@@ -179,10 +179,15 @@ The zone files and Cloudflare now disagree. Fix it, do not leave it.
 3. Run `gh workflow run deploy.yml` and confirm it passes.
 4. Delete the old token in Cloudflare.
 
-### Add somebody to the rotation
+### Add somebody as a reviewer
 
-1. Add them to the `dns-managers` team.
-2. Add their GitHub username to `.github/dns-reviewers.txt` in a pull request.
+Add them to the `dns-managers` team. `CODEOWNERS` points at the team, so that
+is the only step. Check that the team still has write access:
+
+```console
+$ gh api orgs/WITCodingClub/teams/dns-managers/repos/WITCodingClub/dns \
+    --jq .permissions
+```
 
 ### Remove a subdomain