async fn upsert_document(pool: &SqlitePool, item: &SourceItem) -> Result<String>Expand description
Inserts or updates a document in the documents table.
Computes a SHA-256 deduplication hash from the item’s source, source_id,
updated_at timestamp, and body. If a document with the same (source, source_id)
already exists, it is updated with the new data; otherwise a new UUID is assigned.
§Returns
The document’s UUID (existing or newly generated).