Fix AddNewOrder test validation and integration event discovery

[onurnafiguzel]

Fixes #943

Problem

The AddNewOrder functional test in Ordering.FunctionalTests passed even though the
order was never actually created. Issue #943 identified three underlying problems:

1. Validation failures were masked. CreateOrderAsync always returned 200 OK, even
   when the command failed, so an invalid request looked successful.
2. DateTime.Kind mismatch. The test built the card expiration date with
   Convert.ToDateTime(...), producing Kind.Local, which Npgsql rejects for
   timestamp with time zone columns.
3. Integration event types could not be resolved under tests.
   IntegrationEventLogService loaded event types from Assembly.GetEntryAssembly().
   In functional tests the entry assembly is the test host, which does not contain the
   derived IntegrationEvent types, so publishing an order's integration event threw and
   returned 500.

Changes

• OrdersApi.CreateOrderAsync: now returns BadRequest when the command fails,
  consistent with the Cancel/Ship endpoints, instead of always returning Ok.
• IntegrationEventLogService: the assembly to scan for event types is now injected
  via the constructor instead of relying on the entry assembly.
• Ordering.API / Catalog.API DI registration: each API now passes its own
  assembly (typeof(Extensions).Assembly) when registering the log service.
• OrderingApiTests:
  • Renamed the existing invalid-data test to AddNewOrderWithInvalidDataFails
    (asserts BadRequest).
  • Added a new AddNewOrder test using valid data (future UTC expiration date, complete
    address, valid security number) that asserts OK.

Testing

• Ordering.FunctionalTests: 12/12 passing
• Ordering.UnitTests: 41/41 passing

[onurnafiguzel]

@dotnet-policy-service agree