fix: add REDIS_URL to .env and .env.example

.env.example

@@ -8,6 +8,9 @@ DATABASE_POOL_SIZE=10
 DATABASE_IDLE_TIMEOUT_MS=300000
 DATABASE_CONNECT_TIMEOUT_MS=10000
 
+# Redis for rate limits, site-settings cache, and JWT invalidation
+# REDIS_URL=redis://localhost:6379
+
 # Used by SSO ticket generation ({HOTEL_NAME}-{uuid})
 HOTEL_NAME=Atom
 APP_URL=http://localhost:3000