PY-PORT R1: port scripts/lib/dag_status.py to aprender-ci-tools dag-status #4786

Sub-ticket of #4741 (Python helpers ported to the aprender-ci-tools Rust crate). Ports one file.

Port: scripts/lib/dag_status.py → aprender-ci-tools dag-status --root <dir>. It reads the DAG rows as [id, row] JSON pairs on stdin and prints each row's derived status (complete/open, from the leading status: marker of docs/audits/impl-<pmat_id>-receipt.md) plus the D7 lines (a typed status: that disagrees with the receipt).

Acceptance

• The subcommand prints byte-identical stdout and agrees on success/failure with the original over a case table. The original is taken from git as an external validator. The table includes a bad input (a receipt that is not UTF-8, and a row that is not a mapping), a planted mismatch that must be detected, and a declared case count.
• Every caller calls the binary directly, with no new shared Python helper: scripts/render_dag.py, scripts/lib/dag_invariants.py, scripts/session_docs_commit.sh, scripts/pp066_state.sh. check_dag_invariants.sh --selftest, pp066_state.sh --self-test and render_dag.py --check stay green.
• scripts/lib/dag_status.py is deleted.
• Base: the py-port-2/ci-tools branch of PY-PORT-2: port publishable_crates / package_include_diff / coverage_report_scope to Rust (C301) #4741. Branch only until the PR hold lifts.