feat: add apps endpoint with list, get, and batch-get methods

Implement App model and three endpoint methods: list_apps (paginated),
get_app (by ID), and batch_get_apps (up to 100 by IDs). Add
comprehensive tests for success, pagination, not-found, and batch
scenarios.

tests/test_apps.rs

@@ -0,0 +1,120 @@
+mod common;
+
+use wiremock::matchers::{body_json, header, method, path, query_param};
+use wiremock::{Mock, ResponseTemplate};
+
+#[tokio::test]
+async fn test_list_apps_success() {
+    let (mock_server, client) = common::setup().await;
+
+    Mock::given(method("GET"))
+        .and(path("/Apps"))
+        .and(header("x-apikey", "test-api-key"))
+        .and(header("x-api-version", "2"))
+        .respond_with(ResponseTemplate::new(200).set_body_json(serde_json::json!({
+            "pageNumber": 1,
+            "pageSize": 50,
+            "totalPages": 1,
+            "totalRecords": 2,
+            "items": [
+                {"href": "/Apps/id/1", "id": 1, "name": "App One"},
+                {"href": "/Apps/id/2", "id": 2, "name": "App Two"}
+            ]
+        })))
+        .mount(&mock_server)
+        .await;
+
+    let result = client.list_apps(None).await.unwrap();
+    assert_eq!(result.total_records, Some(2));
+    let items = result.items.unwrap();
+    assert_eq!(items.len(), 2);
+    assert_eq!(items[0].id, 1);
+    assert_eq!(items[0].name.as_deref(), Some("App One"));
+}
+
+#[tokio::test]
+async fn test_list_apps_with_paging() {
+    let (mock_server, client) = common::setup().await;
+
+    Mock::given(method("GET"))
+        .and(path("/Apps"))
+        .and(query_param("PageNumber", "2"))
+        .and(query_param("PageSize", "10"))
+        .respond_with(ResponseTemplate::new(200).set_body_json(serde_json::json!({
+            "pageNumber": 2,
+            "pageSize": 10,
+            "totalPages": 3,
+            "totalRecords": 25,
+            "items": []
+        })))
+        .mount(&mock_server)
+        .await;
+
+    let paging = onspring::PagingRequest {
+        page_number: 2,
+        page_size: 10,
+    };
+    let result = client.list_apps(Some(paging)).await.unwrap();
+    assert_eq!(result.page_number, Some(2));
+}
+
+#[tokio::test]
+async fn test_get_app_success() {
+    let (mock_server, client) = common::setup().await;
+
+    Mock::given(method("GET"))
+        .and(path("/Apps/id/42"))
+        .respond_with(ResponseTemplate::new(200).set_body_json(serde_json::json!({
+            "href": "/Apps/id/42",
+            "id": 42,
+            "name": "Test App"
+        })))
+        .mount(&mock_server)
+        .await;
+
+    let app = client.get_app(42).await.unwrap();
+    assert_eq!(app.id, 42);
+    assert_eq!(app.name.as_deref(), Some("Test App"));
+}
+
+#[tokio::test]
+async fn test_get_app_not_found() {
+    let (mock_server, client) = common::setup().await;
+
+    Mock::given(method("GET"))
+        .and(path("/Apps/id/999"))
+        .respond_with(ResponseTemplate::new(404))
+        .mount(&mock_server)
+        .await;
+
+    let result = client.get_app(999).await;
+    assert!(result.is_err());
+    if let Err(onspring::OnspringError::Api { status_code, .. }) = result {
+        assert_eq!(status_code, 404);
+    } else {
+        panic!("Expected Api error");
+    }
+}
+
+#[tokio::test]
+async fn test_batch_get_apps() {
+    let (mock_server, client) = common::setup().await;
+
+    Mock::given(method("POST"))
+        .and(path("/Apps/batch-get"))
+        .and(body_json(serde_json::json!([1, 2, 3])))
+        .respond_with(ResponseTemplate::new(200).set_body_json(serde_json::json!({
+            "count": 3,
+            "items": [
+                {"href": "/Apps/id/1", "id": 1, "name": "App 1"},
+                {"href": "/Apps/id/2", "id": 2, "name": "App 2"},
+                {"href": "/Apps/id/3", "id": 3, "name": "App 3"}
+            ]
+        })))
+        .mount(&mock_server)
+        .await;
+
+    let result = client.batch_get_apps(&[1, 2, 3]).await.unwrap();
+    assert_eq!(result.count, Some(3));
+    assert_eq!(result.items.unwrap().len(), 3);
+}