docs: prepare state store guidance for RocksDB removal - #62

Well-structured deprecation of the RocksDB state-store guide — redirect, nav, and step renumbering all check out, and no stale in-repo links to the deleted page remain. Blocking on two correctness issues: the new verify_snapshot_backend safety check can print PASS on a RocksDB EVM state store, and the new "legacy vs current" data-layout claims contradict this repo's own auto-synced app.toml reference on the same page.