Fix session persistence issue by:
- Using cookies().delete() method for both adminSession and session
- Adding explicit Set-Cookie headers with Max-Age=0 to force browser deletion
- This ensures cookies are cleared both via Next.js API and HTTP headers
Previously, sendBeacon logout calls weren't reliably deleting session cookies,
causing users to remain logged in after closing/reopening the browser.
This double approach ensures the cookies are removed from the browser cache.
Co-Authored-By: Claude Haiku 4.5 <noreply@anthropic.com>
