test: add integration tests for authentication endpoints

[GabrielBBaldez]

Summary

Adds integration tests for the public authentication endpoints (/auth/register, /auth/login, /auth/refresh), addressing #31. The gateway is started on a random port backed by an in-memory R2DBC (H2) database, so each test exercises the full controller → service → repository path end to end (no mocking of the data layer).

Coverage (12 tests):

• register: valid payload, duplicate email, duplicate username, invalid email format, weak password, missing field
• login: valid (by email and by username), wrong password, non-existent user, missing field
• refresh: round-trips a refresh token obtained from login

Drive-by fix: the new tests surfaced that request-validation failures (WebExchangeBindException from @Valid bodies) fell through to the generic handler and returned 500. Added a handler so they now return 400 with the field messages, consistent with the existing ConstraintViolationException handling.

Verified locally with mvn spotless:check test → 13 tests pass.

Resolves #31.

[Copilot]

Pull request overview

Adds end-to-end integration coverage for the API gateway’s public auth endpoints and fixes a validation error-mapping gap so @Valid @RequestBody failures return 400 instead of falling through to the generic 500 handler.

Changes:

• Add GatewayAuthControllerIntegrationTest covering /auth/register, /auth/login, and /auth/refresh.
• Add a WebExchangeBindException handler to return 400 BAD_REQUEST with aggregated field error messages.
• Add test profile R2DBC H2 configuration + test-scoped H2 dependencies to run against an in-memory database.

Reviewed changes

Copilot reviewed 4 out of 4 changed files in this pull request and generated 3 comments.

File	Description
apigateway/src/test/resources/application-test.yaml	Configures in-memory R2DBC H2 and schema initialization for integration tests.
apigateway/src/test/java/vaultweb/apigateway/controller/GatewayAuthControllerIntegrationTest.java	New integration tests for register/login/refresh flows using WebTestClient.
apigateway/src/main/java/vaultweb/apigateway/exceptions/GlobalExceptionHandler.java	Adds handler for WebExchangeBindException to map body validation failures to 400 responses.
apigateway/pom.xml	Adds test dependencies for running R2DBC H2 integration tests.

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[GabrielBBaldez]

Hey @DenizAltunkapan, this one's been sitting for a bit — CI's green and it's mergeable whenever you get a chance to take a look. Thanks!

[DenizAltunkapan]

@GabrielBBaldez thanks for reminding me! it got lost in the emails

[DenizAltunkapan]

@GabrielBBaldez thanks