test(auth): tighten R25 + sign-in controller assertions per code review

Code-quality reviewer flagged:
- R25 'malformed output' tests used .rejects.toThrow(/parse|invalid/i)
  which could match unrelated errors. Replaced with
  .rejects.toBeInstanceOf(ZodError) for both sign-in and sign-up.
- sign-in controller test asserted result.name only as truthy; the
  parallel sign-up test was already precise (toBe('session')). Tightened
  to match.

61 tests still passing for @repo/auth.

packages/auth/src/application/use-cases/sign-in.use-case.test.ts

@@ -1,4 +1,5 @@
 import { describe, it, expect } from "vitest";
+import { ZodError } from "zod";
 import { signInUseCase, signInOutputSchema } from "@/application/use-cases/sign-in.use-case";
 import { MockUsersRepository } from "@/infrastructure/repositories/users.repository.mock";
 import { MockAuthenticationService } from "@/infrastructure/services/authentication.service.mock";
@@ -60,7 +61,7 @@ describe("signInUseCase output validation (R25)", () => {
     } as unknown as IAuthenticationService;
 
     const useCase = signInUseCase(users, auth);
-    await expect(useCase({ username: "alice", password: "x" })).rejects.toThrow(/parse|invalid/i);
+    await expect(useCase({ username: "alice", password: "x" })).rejects.toBeInstanceOf(ZodError);
   });
 
   it("exports an output schema that mirrors the success shape", () => {

packages/auth/src/application/use-cases/sign-up.use-case.test.ts

@@ -1,4 +1,5 @@
 import { describe, it, expect } from "vitest";
+import { ZodError } from "zod";
 import { signUpUseCase, signUpOutputSchema } from "@/application/use-cases/sign-up.use-case";
 import { MockUsersRepository } from "@/infrastructure/repositories/users.repository.mock";
 import { MockAuthenticationService } from "@/infrastructure/services/authentication.service.mock";
@@ -48,7 +49,7 @@ describe("signUpUseCase output validation (R25)", () => {
     const useCase = signUpUseCase(users, auth);
     await expect(
       useCase({ username: "carol", password: "secret_password", confirmPassword: "secret_password" }),
-    ).rejects.toThrow(/parse|invalid/i);
+    ).rejects.toBeInstanceOf(ZodError);
   });
 
   it("exports an output schema that mirrors the success shape", () => {

packages/auth/src/interface-adapters/controllers/sign-in.controller.test.ts

@@ -20,8 +20,7 @@ describe("signInController", () => {
       username: "alice",
       password: "testpassword",
     });
-    expect(result).toBeDefined();
+    expect(result.name).toBe("session");
-    expect(result.name).toBeTruthy();
     expect(result.value).toBeTruthy();
   });