task: #3584504 migrate to shorturl visit event system

Remove DomainAwareVisitMiddleware — the base middleware now collects all X-Shorturl-* headers generically and dispatches a ShortUrlVisitEvent. The VisitDatabaseSubscriber writes them.

Rename header to X-Shorturl-Domain-Id (hyphenated) so the generic header-to-field conversion maps to domain_id column.

Remove middleware class swap from ServiceProvider (only tracker swap remains for direct trackVisit path).

Closes #3584504