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/components/edit-dashboard-button.tsx

@@ -0,0 +1,18 @@
+"use client";
+
+import { usePathname, useRouter } from "next/navigation";
+
+export function EditDashboardButton() {
+  const router = useRouter();
+  const pathname = usePathname();
+
+  return (
+    <button
+      type="button"
+      onClick={() => router.push(`${pathname}?edit=1`)}
+      className="rounded-md border border-input bg-background px-3 py-1.5 text-sm font-medium shadow-sm hover:bg-accent hover:text-accent-foreground transition-colors"
+    >
+      Edit dashboard
+    </button>
+  );
+}