feat(redis): add configurable key namespace prefix (#11042)

Validated on the combined board over tip 80d931ae: quota-redis-store (incl. the KEY_PREFIX derivation test), local-redis-status and rate-limiter-redis-optional green, typecheck:core clean. One pre-merge fix pushed to the branch: docs/reference/ENVIRONMENT.md gained the REDIS_KEY_PREFIX row (env-doc-sync gate requires every .env.example var documented). Board note: the redis tests leave an ioredis retry handle open and hang the runner exit locally — assertions all pass; pre-existing pattern, not from this PR. Thank you @MeRezaRezaei!

.env.example

@@ -87,6 +87,10 @@ DISABLE_SQLITE_AUTO_BACKUP=false
 # Used by: src/shared/utils/rateLimiter.ts
 # Example: redis://localhost:6379 (or redis://redis:6379 in Docker)
 # REDIS_URL=redis://localhost:6379
+# Namespace prefix for ALL OmniRoute Redis keys (rate limiter + auth cache +
+# quota store). Prevents key collisions when OmniRoute shares a Redis instance
+# with other apps (e.g. on 127.0.0.1:6379). Default when unset: omniroute:
+# REDIS_KEY_PREFIX=omniroute:
 # Host interface docker-compose publishes the Redis sidecar on.
 # Default: 127.0.0.1 (loopback only). The compose Redis runs WITHOUT
 # `requirepass`, and app containers reach it over the compose network