docs: record beta68 staging acceptance

[callumalpass]

Summary

• record the merged beta68 Connect/SDK release, signed artifacts, exact staging image digests and rollout held at zero
• record the guarded staging deployment, 15-minute soak, compatibility report and production beta55 boundary
• record coordinated beta68 consumer commits, deployments, CI and authenticated desktop/mobile acceptance
• record migrated 10.2 GB Reader parity, cursor/cancellation/contention/RSS evidence and exact 1/8/128 MiB relay round trips
• record the locked-keyring recovery behavior and interrupted-preflight report-classification follow-ups
• keep the architecture task in progress pending production-readiness review

Validation

• mdbase -C .ops validate reports the task valid with zero issues
• git diff --check

No production deployment is included.