refactor: Feed uses SocialIdentity matching, deps From impl, remove get_accepted_following_urls

Feed builds FollowingFilter by matching SocialIdentity::Local/Remote
instead of URL-prefix heuristic. Removed get_accepted_following_urls
from SocialQuery (no longer needed). Added From<&AppState> for deps
structs — 20 construction sites collapsed to one-liners.

crates/domain/src/ports/noop.rs

@@ -91,9 +91,6 @@ impl super::SocialQuery for NoopSocialQuery {
     async fn is_following(&self, _: &UserId, _: &SocialIdentity) -> Result<bool, DomainError> {
         Ok(false)
     }
-    async fn get_accepted_following_urls(&self, _: &UserId) -> Result<Vec<String>, DomainError> {
-        Ok(vec![])
-    }
 }
 
 // ── NoopFederationAdminQuery ─────────────────────────────────────────────────