Use dynamic port assignment in FakeAuthenticatorHttpClientTest

[Copilot]

Addresses review feedback to prevent test failures from port conflicts. The test was using hardcoded port 8899, which could fail if already in use.

Changes

• Replaced listen(8899) with listen(0) to let the OS assign available ports
• Retrieved actual assigned ports using server.actualPort() after server startup
• Applied to all three server instances: token server, application server, and test HTTP server

// Before
private int port = 8899;
vertx.createHttpServer()
    .requestHandler(tokenServer)
    .listen(port, context.asyncAssertSuccess(server -> {
      log.info("Token server started on port {}", port);
      // ...
    }));

// After
vertx.createHttpServer()
    .requestHandler(tokenServer)
    .listen(0, context.asyncAssertSuccess(server -> {
      int port = server.actualPort();
      log.info("Token server started on port {}", port);
      // ...
    }));

This follows the pattern already used in SampleMain.java, EmailLoginSample.java, and PasswordOnlySample.java.

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