Changes

tsk15: Refactors searchStories endpoint with `contains` param and JSON
errors
This commit refactors the `searchStories` endpoint in `StoryResource` by 
removing the `/search` path and updating the query parameter from `text`
to
`contains`. The corresponding tests were adjusted to use the new
parameter. The endpoint now validates that the `contains` parameter is
provided and not empty, returning a `400 Bad Request` if missing. All
error responses throughout the resource were standardized to JSON
format.