Adds TraktController (GET/POST /api/trakt/lists, GET/PUT/DELETE by id,
POST .../match, GET /api/trakt/status) covering the API gap for SPA
parity issue #142. Add/match/delete dispatch to the same
ChannelWriter<IBackgroundServiceRequest> the classic Blazor "Trakt
Lists" page uses, gated by the existing IEntityLocker (LockTrakt/
IsTraktLocked) singleton; GET /api/trakt/status wraps IsTraktLocked as
the HTTP-observable substitute for the Blazor page's OnTraktChanged
event. URL validation mirrors AddTraktListHandler.ValidateUrl's regexes
(replicated, since that method is private to the handler and returns a
handler-private record) so an obviously-invalid URL gets a synchronous
422 before dispatch.
Adds TraktListResponseModel/PagedTraktListsResponseModel/
TraktStatusResponseModel DTOs, AddTraktListRequest/UpdateTraktListRequest,
controller tests, ApiControllerSecurityTests + OpenApiErrorResponseContractTests
coverage, and regenerates the checked-in OpenAPI document.
