- Rename test_delete_upon_reference_count ->
test_soft_delete_preserves_asset_identity_across_references; the old name
implied last-ref cleanup, but it now verifies the opposite (soft delete
preserves identity across references).
- Strengthen the re-association assertion: also check asset_hash == src_hash
so it proves content reuse rather than relying on the now-tautological
created_new is False.
- Document delete_asset_reference: the orphan-reclamation branch is
intentionally internal-only; the public endpoint always soft-deletes.
- Normalize the soft-delete comment phrasing.
795927b954