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/get_pending.rs

@@ -0,0 +1,15 @@
+use domain::{errors::DomainError, value_objects::{SocialIdentity, UserId}};
+
+use super::{deps::SocialQueryDeps, queries::GetPendingFollowersQuery};
+
+pub async fn execute(
+    deps: &SocialQueryDeps,
+    query: GetPendingFollowersQuery,
+) -> Result<Vec<SocialIdentity>, DomainError> {
+    let user_id = UserId::from_uuid(query.user_id);
+    deps.social_query.get_pending_followers(&user_id).await
+}
+
+#[cfg(test)]
+#[path = "tests/get_pending.rs"]
+mod tests;