feat(wire): attribute updates carry source_execution_id/trace; PullTraceEvents RPC + site read-by-execution-ids

Flow Debugger (design 2026-09-05 §5.3/§5.4): AttributeValueUpdate fields 7/8 stamped by
StreamRelayActor and parsed by SiteStreamGrpcClient (older frames => null/false). New
PullTraceEvents unary RPC on SiteStreamService (same PSK-gated prefix as PullAuditEvents):
a point read of the site audit SQLite by ExecutionId OR ParentExecutionId
(ISiteAuditQueue.ReadByExecutionIdsAsync, json_extract on the codec's camelCase keys, new
IX_audit_event_occurred index, 64-id / 2000-row caps) that moves no cursor and flips no
ForwardState. Central IPullTraceEventsClient/GrpcPullTraceEventsClient mirror the audit pull
client (endpoint resolution, NodeB failover, fault => empty) and register beside it.

Claude-Session: https://claude.ai/code/session_01GSLkkHKz9JrAtmJjmQK3cP

src/ZB.MOM.WW.ScadaBridge.Communication/Actors/StreamRelayActor.cs

@@ -47,7 +47,11 @@ public class StreamRelayActor : ReceiveActor
                 AttributeName = msg.AttributeName,
                 Value = AttributeValueCodec.Encode(msg.Value) ?? string.Empty,
                 Quality = MapQuality(msg.Quality),
-                Timestamp = Timestamp.FromDateTimeOffset(msg.Timestamp)
+                Timestamp = Timestamp.FromDateTimeOffset(msg.Timestamp),
+                // Flow Debugger (design 2026-09-05 §5.3/§5.4): additive fields 7/8 — empty /
+                // false for every change that did not come from a traced write.
+                SourceExecutionId = msg.SourceExecutionId?.ToString("D") ?? string.Empty,
+                Trace = msg.Trace
             }
         };