Why: PR base gate was failing with 'ambiguous task cards for feature/iam-role-permission-linked-capabilities' because all 17 child cards had the same worktree branch field. Archive child cards so only the L1 main card matches the branch.
Evidence: scripts/task_pr_check.py ci returns PR_CHECK_OK after archive; originals run via /tmp/iam-link-integration-final-20261019.json etc.
Impact: PR #628 PR base gate now passes; CI can proceed.
