chore(sync): mirror backend .py + Dockerfile to Space (hf-sync-backend)

docs(cookbook): add SCITT capsule verifier recipe

DEV2: add szl_intoto.py + szl_intoto_routes.py + verify-intoto-receipt.py + patched serve.py (in-toto Statement v1 + Merkle log + verify guide endpoint). Signed-off-by: Stephen Lutar <stephenlutar2@gmail.com>