fix(config): rename costs.config.js to costs.development.config.js

[PierreBrisorgueil]

Problem

modules/costs/config/costs.config.js does not follow the {module}.{env}.config.js naming convention defined in MIGRATIONS.md.

Fix

Rename costs.config.js → costs.development.config.js and update any imports.

Migration note

Add an entry to MIGRATIONS.md documenting the rename so downstream projects know to update their imports if they override this file.

[PierreBrisorgueil]

Fixed in comes-io/trawl_node#653