Save Harbor Saved Query Draft

Creates or completely replaces the mutable draft for a Harbor saved query. Replacement is complete rather than partial. The next validation or publication uses the replacement SQL, parameter declarations, and validation values. Unknown JSON fields, including fields inside parameter declarations, return `400 Bad Request` before the draft is saved. Use `default_value`, not `default`, for parameter defaults. When you omit a parameter during execution, Polytomic uses its published `default_value`, never its draft validation value. An omitted optional parameter without a default binds SQL `NULL`. A required parameter allows omission when a default exists, but rejects explicit `null` even with a default. For a report window, use a required parameter with a default so omission selects a useful window and explicit `null` is rejected: ```json {"name": "days", "type": "number", "required": true, "default_value": 7} ```