feat(auth): signUp publishes userSignedUpEvent

signUpUseCase now takes an IEventBus and publishes userSignedUpEvent
after creating the user (synthesizing email from username since auth
is username-based). Use case mocks-default in module.ts get a fresh
InMemoryEventBus per resolution; bind-production / bind-dev-seed wire
the shared bus passed by bindAll. Tests updated to inject
RecordingEventBus, including a new test that asserts publish on
success and silence on failure.

packages/auth/tests/sign-in-flow.feature.test.ts

@@ -2,6 +2,7 @@
 // Constructs the full chain via direct injection (no container rebinding).
 
 import { describe, it, expect } from "vitest";
+import { RecordingEventBus } from "@repo/core-testing/instrumentation";
 import { MockUsersRepository } from "../src/infrastructure/repositories/users.repository.mock";
 import { MockAuthenticationService } from "../src/infrastructure/services/authentication.service.mock";
 import { signInUseCase } from "../src/application/use-cases/sign-in.use-case";
@@ -18,7 +19,7 @@ describe("auth feature: sign-up → sign-in → sign-out", () => {
     const auth = new MockAuthenticationService(users);
 
     const signIn = signInController(signInUseCase(users, auth));
-    const signUp = signUpController(signUpUseCase(users, auth));
+    const signUp = signUpController(signUpUseCase(users, auth, new RecordingEventBus()));
     const signOut = signOutController(signOutUseCase(auth));
 
     // signUp returns a cookie (presenter shape)