Complete Python doc-sync consolidation (sync_engine covers 3/70 scripts)

Context

PoC landed on branch refactor/python-sync-engine (split out of #1971). It adds a schema-driven scripts/sync_engine.py + scripts/rules/docsync.yaml + scripts/consolidation_schema.md, reproducing 3 of ~70 check_*.py/generate_*.py scripts byte-for-byte (verified: generate_verify_sync_spec, generate_layer2_boundary_catalog, generate_verification_status).

As-is it's dead weight beside the 70 it's meant to replace — "ready" means the engine subsumes them and the originals are deleted with CI switched over.

Remaining work

• Extend docsync.yaml schema to cover the remaining ~67 check/generate scripts.
• For each migrated script: assert byte-identical output against the legacy script (golden diff) before deletion.
• Delete the legacy scripts/check_*.py / scripts/generate_*.py once covered.
• Switch CI to invoke sync_engine.py.

Definition of done

All 70 scripts represented in the schema, legacy scripts removed, CI green on the unified engine, no behavioral drift (golden diffs clean).

Start with scripts/sync_engine.py, scripts/rules/docsync.yaml, and scripts/consolidation_schema.md, then inspect the remaining check_.py and generate_.py scripts. Use the three already reproduced scripts and their byte-identical outputs as the baseline for golden diffs. Done means all 70 scripts are represented, legacy scripts are removed, CI invokes sync_engine.py, and the golden diffs and CI checks pass.