feat(eims): add invoice mapper and signed EIMS transport

Map EDR invoices onto the MoR EIMS /v1/register document and add the
cryptographic transport needed to talk to core.mor.gov.et.

Mapper: DTOs mirror the supplied Postman collection section by section.
Tax is resolved per line via a caller-supplied resolver and throws when
unresolved -- the app models no tax at all (invoice.taxAmount is always 0,
invoice_lines and the rate catalogue carry no fiscal columns), so a
zero-rated default would assert a tax position the codebase cannot support.
Seller identity, document number, counters and previous IRN are passed in
explicitly; the mapper stays pure.

Transport: config, credential loading, RSA-SHA512 signing and /auth/login
with an in-memory token cache. Signing reproduces the process that produced
a working live token -- compact JSON of the inner request only, exact UTF-8
bytes, base64 signature, and base64 of the certificate file's exact bytes
with no parsing or re-encoding. Concurrent callers share one login via an
in-flight promise. Refresh is deliberately unimplemented: the collection
shows an unsigned refresh body but also ships unsigned examples of calls
that do require signing, so an expired token re-logs in instead.

Errors normalise to EimsApiException carrying only the gateway's own error
fields; secrets, signature, certificate and tokens never reach logs.
Key and certificate file patterns are gitignored.

Nothing calls EIMS automatically and no invoice entity, migration or UI is
touched.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>

apps/edr-freight-api/src/app.module.ts

@@ -23,6 +23,7 @@ import databaseConfig from "./config/database.config";
 import telebirrConfig from "./config/telebirr.config";
 import rabbitmqConfig from "./config/rabbitmq.config";
 import faydaConfig from "./config/fayda.config";
+import eimsConfig from "./config/eims.config";
 
 import { BookingsModule } from "./modules/bookings/bookings.module";
 import { ContractsModule } from "./modules/contracts/contracts.module";
@@ -84,6 +85,7 @@ import { PaidImportExportMileDemoSeeder } from "./seed/paid-import-export-mile-d
 //New Trains, Wagons, Container and Cargo management modules
 import { TrainsModule } from "./modules/trains/trains.module";
 import { VerifaydaModule } from "./modules/verifayda/verifayda.module";
+import { EimsModule } from "./modules/eims/eims.module";
 import { FleetHistoryModule } from "./modules/fleet-history/fleet-history.module";
 import { WagonsModule } from "./modules/wagons/wagons.module";
 import { ContainersModule } from "./modules/container-management/containers.module";
@@ -127,6 +129,7 @@ if (!process.env.APPLICATION_NAME) {
         telebirrConfig,
         rabbitmqConfig,
         faydaConfig,
+        eimsConfig,
       ],
     }),
     ScheduleModule.forRoot(),
@@ -248,6 +251,7 @@ if (!process.env.APPLICATION_NAME) {
     InterchangeDocumentsModule,
     ImportOperationsModule,
     VerifaydaModule,
+    EimsModule,
     FleetHistoryModule,
     AiModule,
     AuditModule,