Sync GitLab main through the GitHub gate

[yuezengwu]

What changed

• Synchronize commits created on the temporary self-managed GitLab main branch.
• Preserve commit ancestry so GitHub and GitLab main can converge without force pushes.

Safety

• This PR remains a draft while checks run.
• The synchronization guard marks it ready and merges it only after every check passes.
• The repository review requirement is bypassed only for this checked synchronization PR.
• Merge commit is enabled only for the merge window and immediately disabled again.

Validation

• The guard verified a safe fast-forward relationship or identical file trees.
• GitHub required checks remain authoritative.