Create a saved view

Creates a saved table view for a definition within a space. Authorization: requires space:contribute on :spaceId — lacking it gives 403 (a caller without even space:read gets 404 first). Body: name (required), and optional fields[] ({ fieldKey, isVisible, width, position }), filters[] ({ fieldKey, subField?, operand, value }), sorts[] ({ fieldKey, direction }), filterLogic. Server sets isDefault/spaceId/definitionId. Invalid name/fields/operands → 422 validation_failed. Returns 201 with { view }.