Push new references to existing Wikidata statements

Problem

When enrichment finds a new source that corroborates an existing Wikidata property, a PropertyReference is added to that property (#103). However, there is currently no mechanism to push these new references to the existing Wikidata statement.

This can't happen through the evaluate route — users only evaluate extracted properties (those without statement_id). Existing Wikidata properties are never shown for acceptance, only for rejection in advanced mode. So the reference-pushing needs its own flow.

Expected Behavior

When an existing Wikidata statement accumulates new PropertyReference entries from enrichment, there should be a way to push those as additional reference blocks to the statement via the Wikidata REST API (POST /entities/items/{item_id}/statements/{statement_id}/references).

Notes

• Likely belongs in a dedicated review/push flow rather than the evaluate route
• We already build multi-source reference blocks correctly for new statements
• The push_evaluation "accepted existing statement" branch is currently a no-op and should probably stay that way

Related

• #80 — Add government sources as Wikidata references during enrichment (closed, but the push side was not implemented)
• #103 — Store multiple references per property instead of dropping duplicates

Start by reading the evaluate route and the push_evaluation "accepted existing statement" branch, then trace how PropertyReference entries and multi-source reference blocks are built. Check the existing Wikidata integration against POST /entities/items/{item_id}/statements/{statement_id}/references. Done means a dedicated flow can review and push newly accumulated references to existing statements without changing the no-op branch.