feat: archive a project instead of deleting it

The owner archives a finished project (archiveProject, POST
/projects/{project}/archive) and brings it back (unarchive). While
archived it stays readable, managers still read its rules and webhooks,
but no command changes it: contributing and managing checks refuse with
422, votes and public proposals too, and automations do not run. The web
shows a read-only notice on every page of it (with «Desarchivar» for the
owner), hides what edits, marks it on the home page and lists it last.

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

libs/web/tracker/presenters/src/lib/pages/settings.page.ts

@@ -693,6 +693,32 @@ function idFrom(name: string): string {
       }
 
       @if (facade.isOwner() && facade.project(); as project) {
+        <section
+          class="ts-panel ts-block ts-visibility"
+          aria-labelledby="archive-title"
+        >
+          <div>
+            <h3 id="archive-title">Archivar el proyecto</h3>
+            <p class="ts-muted">
+              @if (project.archivedAt) {
+                Archivado: se puede ver todo, pero nadie puede cambiar nada
+                hasta que lo desarchives.
+              } @else {
+                Para un proyecto terminado: queda todo a la vista (tablero,
+                tickets, historia, estadísticas) y en solo lectura. Se puede
+                desarchivar cuando quieras.
+              }
+            </p>
+          </div>
+          <button
+            type="button"
+            class="ts-secondary"
+            (click)="facade.setArchived(!project.archivedAt)"
+          >
+            {{ project.archivedAt ? 'Desarchivar' : 'Archivar' }}
+          </button>
+        </section>
+
         <section
           class="ts-panel ts-block ts-danger"
           aria-labelledby="danger-title"