refactor(users): content negotiation at GET /users/{username}; move lookup_handler; rename get_me_following

crates/presentation/src/routes.rs

@@ -20,10 +20,7 @@ pub fn router() -> Router<AppState> {
                 .patch(users::patch_profile)
                 .put(users::patch_profile),
         )
-        .route(
-            "/users/me/following-list",
-            get(users::get_me_following_list),
-        )
+        .route("/users/me/following-list", get(users::get_me_following))
         .route("/users/me/top-friends", put(social::put_top_friends))
         // /users/{username} is owned by the AP router (returns AP actor JSON for federation).
         // The REST user profile lives at /users/{username}/profile to avoid the conflict.