Link GitHub release drops to the issues and pull requests they address

Release drops now stay linked to the GitHub issues and pull requests they address. When Hive syncs a GitHub release, it extracts the GitHub references from each drop’s source links, reuses any cached forage records, fetches and stores any missing ones from the connected repositories, and connects them to the drop through a new join table. Closed GitHub items that a release references are preserved in the cache so shipped work remains queryable, and tool responses for a drop now include the linked GitHub issue or pull request metadata, making it possible to answer questions like which release addressed a given forage item.