fix: impersonation navigation uses full page reload

Replace router.push() with window.location.href for both
start and end impersonation to ensure the updated JWT cookie
is sent with the new request. Client-side routing can race
with cookie propagation, causing the server to see the old
session and redirect back to admin.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

src/components/shared/impersonation-banner.tsx

@@ -18,9 +18,8 @@ export function ImpersonationBanner() {
     try {
       await endImpersonation.mutateAsync()
       await update({ endImpersonation: true })
-      toast.success('Returned to admin account')
-      router.push('/admin/members')
-      router.refresh()
+      // Full page navigation to ensure updated JWT cookie is sent
+      window.location.href = '/admin/members'
     } catch (error) {
       toast.error(error instanceof Error ? error.message : 'Failed to end impersonation')
     }