feat(historian): advertise only the backend's aggregates under AggregateFunctions (#682)

IHistorianDataSource.SupportedAggregates (default: every HistoryAggregateType)
is the one authority for both ServerCapabilities/AggregateFunctions (i=2997) and
HistoryServerCapabilities/AggregateFunctions (i=11201) and for the up-front
BadAggregateNotSupported in HistoryRead-Processed. Gateway declares
AggregateModeMapper.Served (4), SqlServer/QuestDB AggregateFamilies.Served (17),
Null none. Only the folder references are trimmed; the SDK's calculator
factories stay so live AggregateFilter subscriptions keep working.

Co-Authored-By: Claude <noreply@anthropic.com>

src/Drivers/ZB.MOM.WW.OtOpcUa.Driver.Historian.Gateway/GatewayHistorianDataSource.cs

@@ -132,6 +132,13 @@ public sealed class GatewayHistorianDataSource : IHistorianDataSource, IAsyncDis
     /// </remarks>
     public bool SupportsReverseEvents => false;
 
+    /// <inheritdoc />
+    /// <remarks>
+    ///     <see cref="AggregateModeMapper.Served"/> — the aggregates the gateway has a retrieval mode for (#682); every
+    ///     other member answers <c>BadAggregateNotSupported</c> and is not advertised.
+    /// </remarks>
+    public IReadOnlySet<HistoryAggregateType> SupportedAggregates => AggregateModeMapper.Served;
+
     /// <inheritdoc />
     /// <remarks>
     ///     A reverse (newest-first) read is refused with <see cref="NotSupportedException"/> — the server reports