GCS free full web search ending 2026-12-31

## Description
GCS free full web search ending 2026-12-31

[Google is discontinuing its free web search index for developers | heise online](https://www.heise.de/en/news/Google-is-discontinuing-its-free-web-search-index-for-developers-11152411.html)
> Google has announced that it will discontinue free access to its full search index for developers. New Programmable Search Engines can now only search a maximum of 50 domains. The previously available "Search the entire web" option will no longer be available for new engines.

[Programmable Search Engine Blog: Updates to our Web Search Products & Programmable Search Engine Capabilities](https://programmablesearchengine.googleblog.com/2026/01/updates-to-our-web-search-products.html):
> **For users of the [Custom Search JSON API](https://developers.google.com/custom-search/v1/overview):** Vertex AI Search is a favorable alternative for up to 50 domains. Alternatively, if your use case necessitates full web search, [contact us](https://docs.google.com/forms/d/e/1FAIpQLSfYcIpOzj57MoetWyeFpJf9Cf4yezG5HDq3VsqbJhlngp5pXw/viewform) to express your interest in and get more information about our full web search solution. Your transition to an alternative solution needs to be completed by **January 1, 2027**.

## Additional context
- `sources.md`: [GCS (Google Custom Search) JSON API](https://github.com/creativecommons/quantifying/blob/main/sources.md#gcs-google-custom-search-json-api)

## Resolution

- [x] I would be interested in resolving this bug.