Fork Backtested Cell

Fork one tested cell of a backtested strategy page into the caller's org.

Reads sources[cell_id] from the committed class P package — the exact program whose numbers the page publishes, a basket headline cell or a per_coin cell (D-30) — and stores it verbatim as a normal DRAFT strategy, through the same bake, validate, lock and upload steps as :func:fork_library_entry.

There is no default cell: an unknown slug or cell is a 404 that names the cells the page does carry (Q-3119: a fork that silently drops its payload is worse than a refusal). A source the validator rejects is a 422.

Provenance: a class P cell is not a library entry, so the library_* columns stay NULL (keel-app links library_source_slug to /library/<slug>). The commit's meta.provenance records {class: P, slug, cell_id, import_id, source_sha256}.