revert: unreviewed registration-lock merge

[NikolayS]

Summary

Revert the unreviewed squash merge of #358.

The implementation was merged without Nik's review or valid merge authorization. This restores main before presenting the fix again in a fresh PR.

Verification

• Revert tree 91d3441bd7995603a58e69de7159393a6497e064
• Pre-merge main tree 91d3441bd7995603a58e69de7159393a6497e064
• git diff --exit-code 15c802c6^1 HEAD passes
• git diff --check HEAD^ HEAD passes

After this revert lands, the registration-lock fix will be recreated as a separate open PR for proper review.

[NikolayS]

Verification and review evidence

Head: 273d6b42c9daf58a08ab8751929901339fa79e1a

• Resulting tree: 91d3441bd7995603a58e69de7159393a6497e064
• Pre-merge main tree (15c802c6^1): 91d3441bd7995603a58e69de7159393a6497e064
• git diff --exit-code 15c802c6^1 HEAD passed
• git diff --check HEAD^ HEAD passed
• CI: 17/17 green after rerunning two Docker Hub connection-timeout jobs

REV was attempted through the installed runner, but its Claude session quota is unavailable until 04:00 UTC. The REV security, bug, test, guidelines, and documentation checks were therefore applied directly to the mechanical revert. No blocking or non-blocking findings: the resulting source tree is byte-for-byte identical to the reviewed repository state immediately before the accidental merge.

The reverted registration bugs are intentionally restored only long enough to present the fix again as a fresh PR for proper review.