WP-01: domain contract and failing tests for auth and user management

Domain entities/ports, service stubs, 18 application unit tests with in-memory
fakes, API integration tests for /api/auth and /api/users, Vitest specs for the
auth store, login page and user form, Playwright auth/user-management flow.

Co-Authored-By: Claude Fable 5.1 <noreply@anthropic.com>

backend/crates/api/tests/users.rs

@@ -0,0 +1,140 @@
+//! WP-01: /api/users routes, admin only.
+mod common;
+
+use axum::http::StatusCode;
+use common::{get, patch, post, test_app_with_admin};
+use serde_json::json;
+
+const ADMIN: &str = "admin@example.com";
+const PW: &str = "admin-password-123";
+
+fn new_user(email: &str) -> serde_json::Value {
+    json!({"email": email, "display_name": "Test User", "password": "user-password-123", "role": "user"})
+}
+
+#[tokio::test]
+async fn admin_can_create_list_get_and_update_users() {
+    let app = test_app_with_admin().await;
+    let token = common::login(&app, ADMIN, PW).await.access;
+
+    let res = post(&app, "/api/users", new_user("u@x.de"), Some(&token)).await;
+    assert_eq!(res.status, StatusCode::CREATED, "{}", res.json);
+    let id = res.json["id"].as_str().unwrap().to_string();
+    assert_eq!(res.json["role"], "user");
+    assert_eq!(res.json["is_active"], true);
+    assert!(res.json.get("password_hash").is_none());
+
+    let list = get(&app, "/api/users", Some(&token)).await;
+    assert_eq!(list.json.as_array().unwrap().len(), 2);
+
+    let one = get(&app, &format!("/api/users/{id}"), Some(&token)).await;
+    assert_eq!(one.json["email"], "u@x.de");
+
+    let upd = patch(
+        &app,
+        &format!("/api/users/{id}"),
+        json!({"display_name": "Renamed", "role": "admin"}),
+        Some(&token),
+    )
+    .await;
+    assert_eq!(upd.status, StatusCode::OK);
+    assert_eq!(upd.json["display_name"], "Renamed");
+    assert_eq!(upd.json["role"], "admin");
+}
+
+#[tokio::test]
+async fn validation_and_conflict_errors_are_mapped() {
+    let app = test_app_with_admin().await;
+    let token = common::login(&app, ADMIN, PW).await.access;
+    let res = post(&app, "/api/users", json!({"email": "bad", "display_name": "x", "password": "user-password-123", "role": "user"}), Some(&token)).await;
+    assert_eq!(res.status, StatusCode::UNPROCESSABLE_ENTITY);
+    assert_eq!(res.json["error"], "validation");
+    let res = post(&app, "/api/users", new_user(ADMIN), Some(&token)).await;
+    assert_eq!(res.status, StatusCode::CONFLICT);
+    assert_eq!(res.json["error"], "email_taken");
+    let res = get(
+        &app,
+        "/api/users/00000000-0000-0000-0000-000000000000",
+        Some(&token),
+    )
+    .await;
+    assert_eq!(res.status, StatusCode::NOT_FOUND);
+}
+
+#[tokio::test]
+async fn last_admin_cannot_be_deactivated() {
+    let app = test_app_with_admin().await;
+    let login = common::login(&app, ADMIN, PW).await;
+    let res = patch(
+        &app,
+        &format!("/api/users/{}", login.user_id),
+        json!({"is_active": false}),
+        Some(&login.access),
+    )
+    .await;
+    assert_eq!(res.status, StatusCode::CONFLICT);
+    assert_eq!(res.json["error"], "last_admin");
+}
+
+#[tokio::test]
+async fn admin_can_reset_password_and_user_can_login_with_it() {
+    let app = test_app_with_admin().await;
+    let token = common::login(&app, ADMIN, PW).await.access;
+    let id = post(&app, "/api/users", new_user("u@x.de"), Some(&token))
+        .await
+        .json["id"]
+        .as_str()
+        .unwrap()
+        .to_string();
+    let res = post(
+        &app,
+        &format!("/api/users/{id}/password"),
+        json!({"password": "brand-new-password"}),
+        Some(&token),
+    )
+    .await;
+    assert_eq!(res.status, StatusCode::NO_CONTENT);
+    let res = post(
+        &app,
+        "/api/auth/login",
+        json!({"email": "u@x.de", "password": "brand-new-password"}),
+        None,
+    )
+    .await;
+    assert_eq!(res.status, StatusCode::OK);
+}
+
+#[tokio::test]
+async fn non_admin_gets_403_on_user_management() {
+    let app = test_app_with_admin().await;
+    let admin = common::login(&app, ADMIN, PW).await.access;
+    post(&app, "/api/users", new_user("u@x.de"), Some(&admin)).await;
+    let user = common::login(&app, "u@x.de", "user-password-123")
+        .await
+        .access;
+
+    assert_eq!(
+        get(&app, "/api/users", Some(&user)).await.status,
+        StatusCode::FORBIDDEN
+    );
+    assert_eq!(
+        post(&app, "/api/users", new_user("v@x.de"), Some(&user))
+            .await
+            .status,
+        StatusCode::FORBIDDEN
+    );
+    // but the user can see themself
+    assert_eq!(
+        get(&app, "/api/auth/me", Some(&user)).await.json["email"],
+        "u@x.de"
+    );
+}
+
+#[tokio::test]
+async fn unauthenticated_requests_are_401() {
+    let app = test_app_with_admin().await;
+    assert_eq!(
+        get(&app, "/api/users", None).await.status,
+        StatusCode::UNAUTHORIZED
+    );
+}