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/unblock.rs

@@ -0,0 +1,18 @@
+use domain::{errors::DomainError, events::DomainEvent, value_objects::UserId};
+
+use super::{commands::UnblockCommand, deps::SocialCommandDeps};
+
+pub async fn execute(deps: &SocialCommandDeps, cmd: UnblockCommand) -> Result<(), DomainError> {
+    let blocker = UserId::from_uuid(cmd.blocker_id);
+    deps.social_command.unblock(&blocker, &cmd.target).await?;
+    deps.event_publisher
+        .publish(&DomainEvent::ActorUnblocked {
+            blocker,
+            target: cmd.target,
+        })
+        .await
+}
+
+#[cfg(test)]
+#[path = "tests/unblock.rs"]
+mod tests;