Fix two pre-existing blockers found during UAT:
- ProfileManagementViewModel: add NotifyCanExecuteChanged on property changes
- SessionManager: open browser in openBrowserCallback (was no-op)
Remaining blocker: SitePickerDialog parsing error from PnP Framework.
Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>
