fix(migrations): duplicate name test fails — unique index missing

[PierreBrisorgueil]

Symptom

modules/core/tests/migrations.integration.tests.js — test "should reject duplicate migration names" fails. recordMigration() resolves instead of rejecting on duplicate names.

Root cause

The Migration model schema likely lacks a unique index on name, so Migration.create() doesn't throw a duplicate key error.

Observed in

• comes-io/trawl_node CI (intermittent, 1/2052 tests)
• Reproduced on master after clean pull

Expected fix

Add unique: true to the name field in the Migration model schema, or add schema.index({ name: 1 }, { unique: true }).