chore(sync): bump simplelogin to v4.81.6

[aio-fleetbot]

Summary

• Updates upstream pins for simplelogin-aio.

What changed

• SimpleLogin: v4.81.4 -> v4.81.6 plus image digest refresh
• Release notes: https://github.com/simple-login/app/releases
• Source repo paths reviewed/generated:
  • Dockerfile

Why

• Keeps the AIO wrapper aligned with upstream while preserving human review.
• Source repo changes are validated here first; catalog sync follows the validated source repo and never starts in awesome-unraid.

Validation

• Generated by aio-fleet upstream monitor; central checks should run on this PR.
• The generated commit must be verified/signed before branch protection allows merge.

Safety assessment

• Safety: warn (0.55 confidence)
• Config delta: none
• Template impact: manifest-targets-present
• Runtime smoke: configured-not-seen
• Next action: runtime/integration tests are configured but no PR runtime check was found
• Review warning: release notes inspection pending on dashboard refresh
• Review warning: runtime/integration tests are configured but no PR runtime check was found
• Dashboard safety state is authoritative after this PR and its checks are visible to aio-fleet.