ci: drop the claim label when an issue closes

A `Closes #N` footer closes the issue on merge and leaves
`Status/In Progress` on it, because Gitea's auto-close touches state
and nothing else. #100 was closed and simultaneously marked as being
actively worked on. `scripts/issue.sh close` does drop the label, and
is exactly the call the footer exists to avoid making.

This hooks the close rather than the merge. Stripping the label in the
PR would work and would be a per-PR habit, which is what the footer
removed in the first place; `issues: [closed]` covers the footer,
issue.sh close and a click in the web UI alike, and asks nothing of
anyone at any of them.

Reopening deliberately does not restore the label: reopening says the
work was not finished, not that somebody is at a keyboard now.

Two costs, both stated in the file rather than discovered later. The
runner has capacity 1 and is shared with an index build that can hold
it for three hours, so this is not instant -- stale for an afternoon
beats stale forever, which is what it was. And it is an eighth
workflow, so CLAUDE.md's count moves with it.

The audit stays, because a workflow that silently stops firing is the
failure mode this area has already produced once:

  ./scripts/issue.sh list --state closed --label "Status/In Progress"

Closes #102

CLAUDE.md

@@ -85,8 +85,18 @@ release decision. The rule that the issue number stays out of the
 still drops the footer. `./scripts/issue.sh list --state open` after a
 merge, looking for what you just shipped; `./scripts/issue.sh close
 <n>` for whatever did not take, with a comment naming the commit.
-`close` also drops `Status/In Progress`, because a claim outlives the
-work if nothing takes the label off.
+
+**Unclaiming is automatic, and it is hooked to the close rather than
+to the merge.** Gitea's auto-close changes state and nothing else, so a
+footer left `Status/In Progress` on a closed issue — #100 was closed
+and marked as being actively worked on at the same time.
+`.gitea/workflows/unclaim.yml` runs on `issues: [closed]`, which covers
+the footer, `issue.sh close` and a click in the web UI alike; stripping
+the label in the PR instead would have been a per-PR habit, and habits
+are what the footer removed. It is not instant — the runner has
+capacity 1 — and reopening deliberately does not restore the label.
+`./scripts/issue.sh list --state closed --label "Status/In Progress"`
+is how you find out it has stopped firing.
 
 ## Planning
 
@@ -2176,10 +2186,11 @@ Pre-commit runs vet, lint, codegen check, and frontend typecheck in parallel. Pr
 
 ## CI
 
-Seven workflows in `.gitea/workflows/`. Five of them package and
+Eight workflows in `.gitea/workflows/`. Five of them package and
 publish (`arch-package`, `homebrew-formula`, `index-artifact`,
 `android-apk`, `desktop-assets`); `release.yml` decides *whether* four of
-those run at all; only `ci.yml` gates, and it is the one to look at when
+those run at all; `unclaim.yml` is housekeeping on the tracker and
+touches no code; only `ci.yml` gates, and it is the one to look at when
 deciding whether a push was healthy.
 
 **`release.yml` is the entry point for all of it.** On every push to