Implement tasks 25, 26 + completion visibility setting

Task 25: Multiple dashboards — dashboards table + migration, /d/[slug]
route, root redirect, dashboard tabs in nav with create/rename/delete/
set-default. Task 26: Editable dashboard — react-grid-layout drag/resize
editor, widget picker modal with per-widget configurator auto-generated
from default config, save/reset server actions with Zod validation.

Completion visibility: server-side per-user setting (hours) replaces
localStorage timer; queries filter completed items by updatedAt cutoff;
Settings page dropdown persists preference via server action.

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

src/app/settings/page.tsx

@@ -34,7 +34,7 @@ export default async function SettingsPage() {
           <CardTitle>Lists</CardTitle>
         </CardHeader>
         <CardContent>
-          <CompletionDelaySetting />
+          <CompletionDelaySetting initialHours={user.completionVisibilityHours} />
         </CardContent>
       </Card>