fix(auth): make local verification portable

Keep upstream identity visible while limiting logout to local auth. Inject the restore privilege gate so the deterministic core tests do not depend on the host OS, and confine descriptor-backed projection tests to Linux. Accept the real remaining Pi timeout budget instead of an exact millisecond.

frontend/src/shell/AppShell.tsx

@@ -716,14 +716,16 @@ export function AppShell({ canLogout }: AppShellProps) {
             <br />
             Human In The Loop
           </p>
-          {authenticatedUser && canLogout && (
+          {authenticatedUser && (
             <div className="mt-4 flex items-center justify-between gap-2 border-t border-border/70 pt-3 text-left">
               <span className="min-w-0 truncate text-xs text-muted-foreground" title={authenticatedUser.displayName ?? authenticatedUser.subject}>
                 {authenticatedUser.displayName ?? authenticatedUser.subject}
               </span>
-              <Button variant="ghost" size="xs" onClick={() => { void signOut().catch(() => undefined); }}>
-                Log out
-              </Button>
+              {canLogout && (
+                <Button variant="ghost" size="xs" onClick={() => { void signOut().catch(() => undefined); }}>
+                  Log out
+                </Button>
+              )}
             </div>
           )}
         </div>