feat(saas): Phase 3 — 模型请求中转服务

- OpenAI 兼容 API 代理 (/api/v1/relay/chat/completions)
- 中转任务管理 (创建/查询/状态跟踪)
- 可用模型列表端点 (仅 enabled providers+models)
- 任务生命周期 (queued → processing → completed/failed)
- 用量自动记录 (token 统计 + 错误追踪)
- 3 个新集成测试覆盖中转端点

crates/zclaw-saas/tests/integration_test.rs

@@ -22,6 +22,7 @@ async fn build_test_app() -> axum::Router {
     let protected_routes = zclaw_saas::auth::protected_routes()
         .merge(zclaw_saas::account::routes())
         .merge(zclaw_saas::model_config::routes())
+        .merge(zclaw_saas::relay::routes())
         .layer(axum::middleware::from_fn_with_state(
             state.clone(),
             zclaw_saas::auth::auth_middleware,
@@ -288,3 +289,63 @@ async fn test_api_keys_lifecycle() {
     // provider 不存在 → 404
     assert_eq!(resp.status(), StatusCode::NOT_FOUND);
 }
+
+// ============ Phase 3: 中转服务测试 ============
+
+#[tokio::test]
+async fn test_relay_models_list() {
+    let app = build_test_app().await;
+    let token = register_and_login(&app, "relayuser", "relayuser@example.com").await;
+
+    // 列出可用中转模型 (空列表，因为没有 provider/model 种子数据)
+    let req = Request::builder()
+        .method("GET")
+        .uri("/api/v1/relay/models")
+        .header("Authorization", auth_header(&token))
+        .body(Body::empty())
+        .unwrap();
+
+    let resp = app.clone().oneshot(req).await.unwrap();
+    assert_eq!(resp.status(), StatusCode::OK);
+    let body_bytes = axum::body::to_bytes(resp.into_body(), MAX_BODY_SIZE).await.unwrap();
+    let body: serde_json::Value = serde_json::from_slice(&body_bytes).unwrap();
+    assert!(body.is_array());
+}
+
+#[tokio::test]
+async fn test_relay_chat_no_model() {
+    let app = build_test_app().await;
+    let token = register_and_login(&app, "relayfail", "relayfail@example.com").await;
+
+    // 尝试中转到不存在的模型
+    let req = Request::builder()
+        .method("POST")
+        .uri("/api/v1/relay/chat/completions")
+        .header("Content-Type", "application/json")
+        .header("Authorization", auth_header(&token))
+        .body(Body::from(serde_json::to_string(&json!({
+            "model": "nonexistent-model",
+            "messages": [{"role": "user", "content": "hello"}]
+        })).unwrap()))
+        .unwrap();
+
+    let resp = app.clone().oneshot(req).await.unwrap();
+    // 模型不存在 → 404
+    assert_eq!(resp.status(), StatusCode::NOT_FOUND);
+}
+
+#[tokio::test]
+async fn test_relay_tasks_list() {
+    let app = build_test_app().await;
+    let token = register_and_login(&app, "relaytasks", "relaytasks@example.com").await;
+
+    let req = Request::builder()
+        .method("GET")
+        .uri("/api/v1/relay/tasks")
+        .header("Authorization", auth_header(&token))
+        .body(Body::empty())
+        .unwrap();
+
+    let resp = app.oneshot(req).await.unwrap();
+    assert_eq!(resp.status(), StatusCode::OK);
+}