Document review-gated PR queue handoff

[ExplodingUFO]

Problem

Several PRs targeting master are implementation-complete with green GitHub checks but remain blocked by the required review gate. The active queue is easy to misread after compaction because bd ready is empty while many open GitHub issues/PRs remain review-gated or stacked.

Scope

Add a narrow tracked handoff document at docs/en/review-gated-pr-queue-handoff.md that records the current review-gated PR queue, the non-bypass rule, and the safe next-action policy for future agent sessions. docs/plans/ is intentionally out of scope because this repository ignores that directory as local planning material.

Acceptance Criteria

• Document lists the current PRs targeting master that are blocked by required review, including PR number, branch, scope, and blocker.
• Document explicitly says not to admin-bypass or merge review-gated PRs without explicit user authorization.
• Document explains why bd ready being empty means no unblocked implementation task should be started from the existing stack.
• Change is isolated to a new tracked docs/en/ markdown file and tracker metadata.
• Verification includes git diff --check and a grep check for the required PR numbers and non-bypass language.

Out of Scope

No code changes, no edits to files currently touched by open PRs, no PR merges, no branch cleanup, no whiteboard implementation work, no CI workflow changes, and no committed docs/plans/ artifact.