feat: runtime manager

lobby/docs/runbook.md

@@ -35,8 +35,11 @@ Before starting the process, confirm:
   - `LOBBY_USER_LIFECYCLE_STREAM` (default `user:lifecycle_events`)
   - `LOBBY_NOTIFICATION_INTENTS_STREAM` (default `notification:intents`)
 - `LOBBY_RACE_NAME_DIRECTORY_BACKEND` is `postgres` for production
-  (the default after PG_PLAN.md §6B); the `stub` value is only for
-  unit tests that do not need a real PostgreSQL.
+  (the default after PG_PLAN.md §6B); the `stub` value selects the
+  in-memory adapter at `lobby/internal/adapters/racenameinmem/`,
+  intended for unit tests and small local deployments without
+  PostgreSQL. The config token name is kept as `stub` for backward
+  compatibility.
 
 At startup the process opens the PostgreSQL pool, applies migrations,
 pings PostgreSQL, then opens the Redis client and pings Redis. Startup