~x-ai/grok-latest → A (3:1)

Commit A adds a full RocksDB-backed durable crate, moves Reddit entity JSON off the in-memory GlobalTree into entity_db, and streams event-log replay line-by-line, which is a lasting architectural fix for startup RAM and payload retention. Commit B correctly stabilizes feed catch-up on ingest order and hardens multi-user private-room visibility with solid tests, but it is a targeted correctness fix in one API path rather than a foundational storage redesign.