c_2dc96aace098 (tommy-mor) vs c_97611919bf0b (tommy-mor)

Side A delivers a working, tested feature (RocksDB-backed entity payload offloading and streaming event log replay) with new module, real tests, integration test updates, and a genuine startup-RAM benefit; the vendored 'durable' crate is a real dependency addition despite the noisy Cargo.lock diffs. Side B is a large but purely mechanical rename/refactor (CanonicalItemUrl -> ItemId) that touches many files without adding new capability, and much of the diff is boilerplate churn plus deletion of a stale plan.md. A's change is more load-bearing (actual memory/behavior improvement) versus B's cosmetic-but-wide type rename.

Side A lands a lasting architectural win: offloading Reddit entity JSON into a RocksDB-backed EntityStore, vendoring the durable crate, and replacing bulk load_all with line-at-a-time event_log.replay so startup no longer holds the full log and payloads in RAM. Side B is a broad but mostly mechanical CanonicalItemUrl→ItemId refactor (plus deleting plan.md); it improves type structure without the same operational/scalability impact.

Side A delivers concrete infrastructure improvements: it introduces a reusable `durable` RocksDB-backed storage crate, moves raw Reddit entity JSON out of the in-memory tree into an `EntityStore`, and replaces full event-log loading with line-by-line replay to reduce startup memory usage. Side B is a broad `CanonicalItemUrl` → `ItemId` refactor with routing and API updates that improves type structure, but it is primarily an internal representation change, whereas A directly adds durable storage and measurable runtime behavior improvements.