refactor

docs/api_responses.md

@@ -0,0 +1,17 @@
+# API response helpers
+
+The backend now exposes `crate::http::responders`, which wraps common success and
+error patterns for routes:
+
+- `ok_json`, `created_json`, `accepted_json` return `JsonResponse<T>` with the
+  respective status codes.
+- `no_content`/`empty` provide shared empty responses.
+- `JsonResponse<T>` implements `IntoResponse`, so any handler can return
+  `AppResult<JsonResponse<T>>` without pairing tuples manually.
+- `IntoAppResult`, `RowsAffectedExt`, and friends convert Diesel results into
+  `AppResult<T>` with consistent `AppError` handling.
+
+When adding new routes, import from `crate::http::responders` instead of
+constructing `(StatusCode, Json<T>)` tuples directly. The folders, documents,
+auth, capability-set, correspondent, tag, and profile routers now all share
+these helpers; WebDAV keeps its bespoke streaming responses for now.