Conditional formatting: accept Excel's operator names, refuse unknown ones

home.conditionalFormat took any operator it didn't know as "greater",
so a Cell Value rule given Excel's own names (lessThan, greaterThan,
lessThanOrEqual, greaterThanOrEqual, as in the file format and VBA)
silently became "greater than". Those names are now accepted, as data
validation already does, and anything else is an error.

crates/engine/src/cmd/insert.rs

@@ -1157,15 +1157,17 @@ fn add_cf(s: &mut Session, p: &Json) -> Result<Json> {
     };
     let rule = match kind.as_str() {
         "cellIs" => {
+            // Excel's file and VBA names (`lessThan`, …) are accepted too.
             let op = match g("operator").as_deref().unwrap_or("greater") {
                 "between" => CfOperator::Between,
                 "notBetween" => CfOperator::NotBetween,
                 "equal" => CfOperator::Equal,
                 "notEqual" => CfOperator::NotEqual,
-                "less" => CfOperator::Less,
-                "greaterOrEqual" => CfOperator::GreaterOrEqual,
-                "lessOrEqual" => CfOperator::LessOrEqual,
-                _ => CfOperator::Greater,
+                "less" | "lessThan" => CfOperator::Less,
+                "greaterOrEqual" | "greaterThanOrEqual" => CfOperator::GreaterOrEqual,
+                "lessOrEqual" | "lessThanOrEqual" => CfOperator::LessOrEqual,
+                "greater" | "greaterThan" => CfOperator::Greater,
+                other => return Err(bad("home.conditionalFormat", format!("unknown operator `{other}`"))),
             };
             let a = rule.get("value").map(super::edit::json_to_input).unwrap_or_default();
             let b = rule.get("value2").map(super::edit::json_to_input);