write the missing sidecar for this receipt

This receipt carried no .sha256 companion, so nothing could verify it on a
fresh clone. The sidecar records the hash of the bytes as they are stored now.

It does not assert the receipt was correct when written - only that these are
the bytes, so any future change becomes visible instead of silent. Written only
where no sidecar existed; nothing already recorded was replaced.

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>

OCCURRENCES.hbi.sha256

@@ -0,0 +1 @@
+38880d4f474be16c2d036e122dc9fb884c84466d58e7fcb1ff3ba7ef946438b3  OCCURRENCES.hbi