refactor: consolidate 11 social use cases → SocialCmd/SocialQry enum dispatch

-280 net lines. 11 one-file use cases replaced by execute_command/
execute_query with enum dispatch. Added FollowRejected event (reject
was silently dropping). Command→event mapping now explicit in one match.

crates/application/src/social/get_followers.rs

@@ -1,18 +0,0 @@
-use domain::{
-    errors::DomainError,
-    value_objects::{SocialActor, UserId},
-};
-
-use super::{deps::SocialQueryDeps, queries::GetFollowersQuery};
-
-pub async fn execute(
-    deps: &SocialQueryDeps,
-    query: GetFollowersQuery,
-) -> Result<Vec<SocialActor>, DomainError> {
-    let user_id = UserId::from_uuid(query.user_id);
-    deps.social_query.get_followers(&user_id).await
-}
-
-#[cfg(test)]
-#[path = "tests/get_followers.rs"]
-mod tests;