implement exchange settings management and fallback rate handling

apps/edr-freight-api/src/migrations/3240000000000-CreateExchangeSettings.ts

@@ -0,0 +1,45 @@
+import { MigrationInterface, QueryRunner, Table } from 'typeorm';
+
+/**
+ * Single-row store for the USD→ETB fallback used when the CBE exchange-rate
+ * endpoint is unreachable. The live CBE rate always wins; every successful
+ * fetch overwrites this row, so it holds the last known good rate rather than
+ * a constant that drifts. Operators can also set it by hand during an outage.
+ *
+ * Seeded with the CBE USD transactional selling rate on 2026-08-04, so the
+ * fallback is usable before the first successful fetch.
+ */
+export class CreateExchangeSettings3240000000000 implements MigrationInterface {
+  name = 'CreateExchangeSettings3240000000000';
+
+  public async up(queryRunner: QueryRunner): Promise<void> {
+    await queryRunner.createTable(
+      new Table({
+        schema: 'freight',
+        name: 'exchange_settings',
+        columns: [
+          { name: 'id', type: 'uuid', isPrimary: true, generationStrategy: 'uuid', default: 'gen_random_uuid()' },
+          { name: 'fallback_rate', type: 'numeric', precision: 18, scale: 6 },
+          // AUTO when written by the CBE sync, MANUAL when set in the backoffice.
+          { name: 'fallback_source', type: 'varchar', length: '16', default: "'AUTO'" },
+          { name: 'last_synced_at', type: 'timestamptz', isNullable: true },
+          // IAM user id (iam.users) — no FK, iam schema is externally owned.
+          { name: 'updated_by_id', type: 'uuid', isNullable: true },
+          { name: 'created_at', type: 'timestamptz', default: 'now()' },
+          { name: 'updated_at', type: 'timestamptz', default: 'now()' },
+          { name: 'deleted_at', type: 'timestamptz', isNullable: true },
+        ],
+      }),
+      true,
+    );
+
+    await queryRunner.query(`
+      INSERT INTO freight.exchange_settings (fallback_rate, fallback_source)
+      VALUES (162.416500, 'AUTO')
+    `);
+  }
+
+  public async down(queryRunner: QueryRunner): Promise<void> {
+    await queryRunner.dropTable('freight.exchange_settings', true);
+  }
+}