Real-time UI Progress for Ingestion (WebSockets/SSE)

[b08x]

Since ingestion handles bulk files asynchronously (#56), the Document Upload Dashboard (#30) requires real-time progress updates. Implement WebSockets or Server-Sent Events (SSE) between the Roda backend and the frontend to stream status updates.

[b08x]

Architectural Decision: Real-time UI progress will query Redis (via Ohm sets) to get instant counts of 'pending' vs 'done' jobs, avoiding heavy read-load on Postgres while it is busy writing vectors.