Delay item disappearance after check-off; add setting in Settings

Items on the lists page and dashboard widget now show as crossed-out for
a configurable duration (default 3s) before vanishing. Unchecking within
the window cancels the removal. The delay is stored in localStorage and
configurable via Settings → Lists (options: 1s / 3s / 5s / 10s / 30s).

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

src/app/settings/page.tsx

@@ -4,6 +4,7 @@ import { getEntityType } from "@/modules/_core/registry";
 import { Card, CardContent, CardHeader, CardTitle } from "@/components/ui/card";
 import { Button } from "@/components/ui/button";
 import { ThemePicker } from "@/components/theme-picker";
+import { CompletionDelaySetting } from "@/components/completion-delay-setting";
 import { revokeShareLinkAction } from "./actions";
 import Link from "next/link";
 
@@ -28,6 +29,15 @@ export default async function SettingsPage() {
         </CardContent>
       </Card>
 
+      <Card>
+        <CardHeader>
+          <CardTitle>Lists</CardTitle>
+        </CardHeader>
+        <CardContent>
+          <CompletionDelaySetting />
+        </CardContent>
+      </Card>
+
       <Card>
         <CardHeader>
           <CardTitle>Active Share Links</CardTitle>