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/modules/eims/eims.module.ts

@@ -0,0 +1,19 @@
+import { HttpModule } from "@nestjs/axios";
+import { Module } from "@nestjs/common";
+import { EimsAuthService } from "./eims-auth.service";
+import { EimsClientService } from "./eims-client.service";
+import { EimsCredentialsProvider } from "./eims-credentials.provider";
+import { EimsSignerService } from "./eims-signer.service";
+
+/**
+ * MoR EIMS e-invoicing transport. Exports only what other modules will consume; the credential
+ * loader and signer stay internal so the private key has exactly one user.
+ */
+@Module({
+  imports: [
+    HttpModule.register({ timeout: Number(process.env.EIMS_HTTP_TIMEOUT_MS) || 30_000 }),
+  ],
+  providers: [EimsCredentialsProvider, EimsSignerService, EimsAuthService, EimsClientService],
+  exports: [EimsAuthService, EimsClientService],
+})
+export class EimsModule {}