refactor: eliminate User/UserResponse struct literals, add AP user tests

- Feed/search adapters use #[sqlx(flatten)] UserRow instead of
  inline User construction — single point of change when User
  gains fields
- User::new_remote constructor replaces struct literal in testing
- to_summary_response replaces inline UserResponse in get_users
- 5 integration tests for PgApUserRepository (find, count,
  profile_fields→attachment)

crates/presentation/src/handlers/auth.rs

@@ -5,6 +5,7 @@ use api_types::{
 };
 use application::use_cases::auth::{login, register, LoginInput, RegisterInput};
 use axum::{http::StatusCode, response::IntoResponse, Json};
+use domain::models::feed::UserSummary;
 use domain::ports::{AuthService, EventPublisher, PasswordHasher, UserRepository};
 
 deps_struct!(AuthDeps {
@@ -37,6 +38,22 @@ pub fn to_user_response(u: &domain::models::user::User) -> UserResponse {
     }
 }
 
+pub fn to_summary_response(u: &UserSummary) -> UserResponse {
+    UserResponse {
+        id: u.id.as_uuid(),
+        username: u.username.clone(),
+        display_name: u.display_name.clone(),
+        bio: u.bio.clone(),
+        avatar_url: u.avatar_url.clone(),
+        header_url: None,
+        custom_css: None,
+        profile_fields: vec![],
+        local: true,
+        is_followed_by_viewer: false,
+        created_at: chrono::Utc::now(),
+    }
+}
+
 #[utoipa::path(
     post, path = "/auth/register",
     request_body = RegisterRequest,

crates/presentation/src/handlers/users/mod.rs

@@ -1,7 +1,7 @@
 use crate::{
     errors::ApiError,
     extractors::{AuthUser, Deps, FromAppState, OptionalAuthUser},
-    handlers::auth::to_user_response,
+    handlers::auth::{to_summary_response, to_user_response},
     state::AppState,
 };
 use api_types::{
@@ -200,23 +200,7 @@ pub async fn get_users(
     }
 
     let result = list_users(&*d.users, page_params).await?;
-    let items: Vec<UserResponse> = result
-        .items
-        .iter()
-        .map(|u| UserResponse {
-            id: u.id.as_uuid(),
-            username: u.username.clone(),
-            display_name: u.display_name.clone(),
-            bio: u.bio.clone(),
-            avatar_url: u.avatar_url.clone(),
-            header_url: None,
-            custom_css: None,
-            profile_fields: vec![],
-            local: true,
-            is_followed_by_viewer: false,
-            created_at: chrono::Utc::now(),
-        })
-        .collect();
+    let items: Vec<UserResponse> = result.items.iter().map(to_summary_response).collect();
     Ok(Json(PagedResponse {
         items,
         total: result.total,