gstack-pregate clear and gstack-tree-receipt now classify through one
classifyFiles, so under changelog_fragments a receipt for the fragment head
clears the stamped head when the stamp is exactly the fold. The ship-policy
reference names ready's receipt push, land's own check polling, the key-off
refusal and the /ship changelog_fragments line.
Co-authored-by: capy-ai[bot] <230910855+capy-ai[bot]@users.noreply.github.com>