fix(xlsx): complete pivot calculatedField end-to-end (known prop)

_knownPivotKeys was missing calculatedField / calculatedFields, so
even though ApplyCalculatedFields wired up the cacheField + dataField
+ calculatedFields block, the Add pipeline still warned 'UNSUPPORTED
props: calculatedField' to stderr. Add both keys to the known set and
strip trailing digits in CollectUnknownPivotKeys so numbered variants
(calculatedField1, calculatedField2, ...) also match. Expose the
check as a public IsKnownPivotProperty helper for tests.

src/officecli/Core/PivotTableHelper.cs

@@ -221,6 +221,10 @@ internal static partial class PivotTableHelper
             // PV7: labelFilter=field:type:value — row-level pre-cache filter
             // (see ApplyLabelFilter).
             "labelfilter",
+            // R4-3: calculatedField[N]=Name:=Formula — numbered variants are
+            // also accepted; CollectUnknownPivotKeys normalizes trailing
+            // digits before the known-set check.
+            "calculatedfield", "calculatedfields",
         };
 
     /// <summary>
@@ -240,12 +244,28 @@ internal static partial class PivotTableHelper
         {
             if (string.IsNullOrEmpty(key)) continue;
             var canonical = NormalizePivotPropKey(key);
-            if (!_knownPivotKeys.Contains(canonical))
+            // R4-3: strip trailing digits before lookup so `calculatedField1`,
+            // `calculatedField2`, etc. match the canonical `calculatedfield`.
+            var stripped = System.Text.RegularExpressions.Regex.Replace(canonical, @"\d+$", "");
+            if (!_knownPivotKeys.Contains(canonical)
+                && !_knownPivotKeys.Contains(stripped))
                 unknown.Add(key);
         }
         return unknown;
     }
 
+    /// <summary>
+    /// Public wrapper around <see cref="_knownPivotKeys"/> + alias/digit
+    /// normalization for tests and external callers.
+    /// </summary>
+    public static bool IsKnownPivotProperty(string key)
+    {
+        if (string.IsNullOrEmpty(key)) return false;
+        var canonical = NormalizePivotPropKey(key);
+        var stripped = System.Text.RegularExpressions.Regex.Replace(canonical, @"\d+$", "");
+        return _knownPivotKeys.Contains(canonical) || _knownPivotKeys.Contains(stripped);
+    }
+
     /// <summary>
     /// Emit an UNSUPPORTED props warning to stderr for the Add pivot path.
     /// Set already surfaces unknown keys through its return list; Add has