refactor: move federation port types from adapter to domain

ActivityPubRepository→FederationContentRepository,
OutboundFederationPort→FederationBroadcastPort,
ActorApUrls→ActorFederationUrls.

Removes activitypub dep from application and presentation crates.
Adapter re-exports old names as aliases for backward compat.
Also fixes count_users test broken by instance actor migration.

crates/presentation/Cargo.toml

@@ -5,7 +5,6 @@ edition = "2021"
 
 [dependencies]
 domain           = { workspace = true }
-activitypub      = { workspace = true }
 application      = { workspace = true }
 api-types   = { workspace = true }
 axum        = { workspace = true }