feat: unified social identity layer — SocialIdentity, ports, use cases, adapter

SocialIdentity value object (Local|Remote), SocialCommand/SocialQuery
domain ports, 11 CQRS use cases w/ 14 tests, CompositeSocialAdapter
wrapping k_ap, 6 new domain events, handlers migrated from ap_service
to use cases. Closes #12 foundation — AP handlers + legacy cleanup TBD.

crates/application/src/social/tests/accept.rs

@@ -0,0 +1,59 @@
+use std::sync::Arc;
+
+use domain::{
+    events::DomainEvent,
+    testing::{InMemorySocialRepository, NoopEventPublisher},
+    value_objects::{SocialIdentity, UserId},
+};
+use uuid::Uuid;
+
+use crate::social::{
+    accept,
+    commands::{AcceptFollowCommand, FollowCommand},
+    deps::SocialCommandDeps,
+    follow,
+};
+
+fn make_deps() -> (Arc<InMemorySocialRepository>, Arc<NoopEventPublisher>, SocialCommandDeps) {
+    let social = InMemorySocialRepository::new();
+    let events = NoopEventPublisher::new();
+    let deps = SocialCommandDeps {
+        social_command: Arc::clone(&social) as _,
+        social_query: Arc::clone(&social) as _,
+        event_publisher: Arc::clone(&events) as _,
+    };
+    (social, events, deps)
+}
+
+#[tokio::test]
+async fn accept_follow_emits_follow_accepted_event() {
+    let (_social, events, deps) = make_deps();
+    let follower_id = Uuid::new_v4();
+    let owner_id = Uuid::new_v4();
+    let requester = SocialIdentity::Local(UserId::from_uuid(follower_id));
+
+    follow::execute(
+        &deps,
+        FollowCommand {
+            follower_id,
+            target: SocialIdentity::Local(UserId::from_uuid(owner_id)),
+        },
+    )
+    .await
+    .unwrap();
+
+    accept::execute(
+        &deps,
+        AcceptFollowCommand {
+            owner_id,
+            requester,
+        },
+    )
+    .await
+    .unwrap();
+
+    let published = events.published();
+    assert!(published
+        .iter()
+        .any(|e| matches!(e, DomainEvent::FollowAccepted { .. })));
+}