feat: remove the 10,000-character article body limit and make the New article body optional

docs/design/screens/integration.md

@@ -42,8 +42,8 @@ Plain text, one sentence. Used in the table and in the per-endpoint error captio
 - 413 and 415 on `POST /v1/media/` keep their earlier plain captions; no real message is known.
 
 ## Request bodies
-- `POST /v1/article/`: `title` (string, required, 3 to 200 characters), `body` (string, required, max 10000 today; the limit is being removed, see change-list.md item 3).
-- `PATCH /v1/article/{id}`: `body` (string, required, max 10000 today; same).
+- `POST /v1/article/`: `title` (string, required, 3 to 200 characters), `body` (string, optional, no length limit).
+- `PATCH /v1/article/{id}`: `body` (string, optional, no length limit).
 - `PATCH /v1/media/{id}` (rename): `filename` (string, required).
 - `POST /v1/media/merge`: `keep_id` (number, required, > 0), `merge_ids` (number[], required, at least 1, each > 0).
 - `POST /v1/media/`: multipart/form-data, 1 file field (shown as "multipart/form-data, 1 file field").