feat: definition of done per project

A project can ask that tickets reach a DONE status only with their
checklist ticked (settings.checklistBeforeDone, off by default; absent
when saving means unchanged). Members get a 422 telling how many steps are
left; owners and admins may still close it. Settings has the switch and
the ticket's checklist says when the project asks for it.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

libs/web/tracker/presenters/src/lib/pages/issue.page.scss

@@ -231,6 +231,12 @@ a.ts-key {
   white-space: nowrap;
 }
 
+.ts-checklist__rule {
+  margin: 0 0 0.5rem;
+  color: var(--ts-muted);
+  font-size: 0.8125rem;
+}
+
 .ts-checklist,
 .ts-children {
   display: grid;