Add sharing links for fires

Add ability to share a file with a URL link. This would allow a fire to be delivered to a client that requests it without them having to search for it.

The link would populate the applicable search fields and select the fire

No files, tests, or entry points are named. Start by tracing the frontend's search-field state and fire-selection flow, then determine how URLs are currently handled. Done means a sharing URL opens the application with the applicable search fields populated and the requested fire selected.

Written by the indexing model from the issue text.