Train: REM methodology v2.4 — docs & API

What: The REM (Rail Emission Model) train methodology is documented as the primary rail integration path. methodology: "REM" replaces "SQUAKE" in examples (legacy alias still accepted). Integration docs and OpenAPI train schemas now include departure_date (ISO YYYY-MM-DD), origin_country / destination_country (ISO 3166-1 alpha-2), energy_scope (wtw / ttw), optional route_coords for border-aware distance, and the tiered factor resolver (Tier 1 → Tier 3 → Tier 4 → Tier 5; Tier 2 is not used in production).

Do now: Use Train: REM for field definitions and request shapes; prefer REM in new integrations.

Reference: REM factor bundle and loader notes are maintained alongside the calculation service; methodology narrative follows REM v2.4.