fix: use semantic colors across admin pages

src/app/admin/calendar/[id]/page.tsx

@@ -132,7 +132,7 @@ export default async function AdminCalendarCampaign({ params }: { params: Promis
           </thead>
           <tbody>
             {rewards.map((r) => (
-              <tr key={r.id} className="border-t border-[var(--border-subtle)]">
+              <tr key={r.id} className="border-t border-[var(--admin-border)]">
                 <td>{r.id}</td>
                 <td>
                   {r.productName || <span className="text-sm theme-text-muted dark:theme-text-muted">—</span>}