GHSA-jj6q-rrrf-h66h: OpenClaw: Shared-secret comparison call sites leaked length information through timing

OpenClaw versions before 2026.4.2 had a timing side channel (a security weakness where an attacker can learn secret information by measuring how long operations take) in shared-secret comparison code. The vulnerability could leak information about the length of secrets through measurable timing differences, though it didn't directly allow attackers to bypass authentication.