Support single-witness data entry

When a contributor has a single document that will serve as the basis for many new glosses, there should be a simple path to just identify new fragments that co-create new Named Glosses without requiring extra steps. This should be established as its own workflow and reuse the data as appropriate.

No file, test, or entry point is identified in the issue. Start by mapping the existing data-entry workflow and how documents, fragments, and Named Glosses are currently connected. Done means a separate single-witness workflow can identify new fragments and create related Named Glosses without the extra steps used for other entries.

Written by the indexing model from the issue text.