Images Like This

[ellenmuller]

What does this change?

This PR adds a 'More Like This' feature to the Grid, enabling users to find
visually and semantically similar images from within the image library.

It builds on the existing semantic search functionality by introducing:

• s3vectors.searchByImage — a new method that queries S3 vector storage using
  an image as the search input
• embedder.imageToImageSearch — a higher-level wrapper called from Media API

In Media API, requests are checked for the similar: <image id> query type to
qualify them as similarity searches. This query is automatically populated when
the user clicks 'More Like This' on any image.

⚠️ Known issue: The 'Use AI Search' toggle behaves unexpectedly when
switching between search modes. This will be addressed before merge.

How should a reviewer test this change?

1. Navigate to the Grid and open any image
2. Click the 'More Like This' button
3. Verify that a set of visually similar images is returned
4. Try switching between similarity search and regular search modes — note the
   known issue with the 'Use AI Search' toggle (see above)

How can success be measured?

• Clicking 'More Like This' consistently returns visually relevant results
• No regressions in existing semantic search behaviour

Tested? Documented?

• locally by committer
• locally by Guardian reviewer
• on the Guardian's TEST environment
• relevant documentation added or amended (if needed)

[github-actions]

Deploy build 14175 of media-service::grid::all to TEST

All deployment options

• Deploy build 14175 of media-service::grid::all to TEST
• Deploy parts of build 14175 to TEST by previewing it first
• What's on TEST right now?

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From guardian/actions-riff-raff.