When a session expires, the user's current URL is now captured and restored
after re-authentication (via remember-me cookie or manual login), instead of
always redirecting to the dashboard. A JavaScript session warning dialog
appears ~2 minutes before idle timeout, allowing users to extend their session
with a single click. Includes open-redirect prevention via URL validation,
Microsoft SSO callback support, and 33 unit tests.
Refs: SESSION-REDIRECT-PRESERVE-001
Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>
