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.

Cargo.lock

@@ -273,7 +273,6 @@ dependencies = [
 name = "application"
 version = "0.1.0"
 dependencies = [
- "activitypub",
  "async-trait",
  "bytes",
  "chrono",
@@ -2605,7 +2604,6 @@ dependencies = [
 name = "presentation"
 version = "0.1.0"
 dependencies = [
- "activitypub",
  "api-types",
  "application",
  "async-trait",