Two content conflicts, both from main splitting the files this branch edits.
crates/cos/src/document.rs: main moved Document into document/*.rs.
Keep that split. A missing /ID is still pdfcraft_crypt::file_id of the
encryption seed (document/open.rs); generated_id is gone. The regression
lives in document/tests.rs.
crates/engine/src/edit.rs: main moved EditCtx and run_edit into
edit/run.rs. Keep that split. Protect still draws its seed and default
owner password from getrandom on EditCtx and fails closed
(EditError::Protection) when the CSPRNG errors or returns all zeros.
Co-authored-by: jonathanwxh-cell <jonathanwxh-cell@users.noreply.github.com>