* test(image-search): expect source_url in DuckDuckGo and Serper results
* fix(image-search): keep the source page URL in DuckDuckGo and Serper results
The DuckDuckGo and Serper image_search tools returned only title,
image_url and thumbnail_url and dropped the page each image comes from
(DDGS `url`, Serper `link`). Brave already returns it as `source_url`,
and the workspace UI links every image thumbnail through `source_url`,
so DuckDuckGo (the default provider) and Serper results rendered as
"Unsafe link omitted" and the agent lost the image's source page.
Return `source_url` from both providers, screened with
`safe_public_result_url` like the image and thumbnail URLs.
