Get Memory Status

Get processing status for a memory item.

Returns the current processing lifecycle stage:
- `queued` — Accepted, waiting to be processed
- `quick_saved` — Quick add complete (stored in DB + vector store), background processing pending
- `processing` — Background processing in progress (graph indexing, Neo4j nodes, enrichment)
- `completed` — All processing finished
- `failed` — Processing failed

Use this endpoint to poll for completion after adding a memory.
For real-time updates, connect to WebSocket at `/ws/memory-status/{memory_id}`.