docs(snowflake): document managed db/schema property ownership

Author: HandSonic

chat2db-community-server/chat2db-community-plugins/chat2db-community-snowflake/src/main/java/ai/chat2db/plugin/snowflake/SnowflakeDBManager.java

@@ -47,6 +47,10 @@ static List<KeyValue> prepareExtendInfo(ConnectInfo connectInfo) {
         return extendInfo;
     }
 
+    // `db` and `schema` are managed keys owned by the connection form's databaseName/schemaName:
+    // they are always dropped (including manually added entries) before the current value is
+    // written back, so clearing a field cannot keep stale context. Configure the Snowflake
+    // database/schema through the connection fields, not through extendInfo.
     private static void replacePropertyIfConfigured(List<KeyValue> extendInfo, String propertyName, String propertyValue) {
         // Always drop the managed entry first so a reused ConnectInfo cannot keep a stale value after it is cleared.
         removeProperty(extendInfo, propertyName);