feat(siteeventlog): emit store_and_forward + notification events (M1.7)

StoreAndForwardService gains an optional ISiteEventLogger? ctor param (default
null so the many direct-construction tests still compile) and, when wired,
mirrors its own buffer/retry/park activity onto site operational events via the
existing OnActivity hook (which already isolates a throwing subscriber, so a
failing event log can never be misclassified as a transient delivery failure):

- store_and_forward (ExternalSystem / CachedDbWrite): queued/retried/delivered/
  parked. Warning on buffer/retry, Error on park, Info on retry-recovery; an
  immediate-success delivery is the hot path and is not logged.
- notification (the site forward-to-central path): logged ONLY on forward
  FAILURE (buffered after the immediate forward threw) and on park, per the
  Component-SiteEventLogging spec — routine enqueue and forward-success are
  deliberately not logged (central's Notifications table is the audit record).

Wired through AddStoreAndForward (resolves ISiteEventLogger optionally from DI);
StoreAndForward project now references SiteEventLogging (acyclic: SiteEventLogging
references only Commons). Also documents the 'notification' category on the
ISiteEventLogger.LogEventAsync eventType param (folds in M1.8 doc fix).

src/ZB.MOM.WW.ScadaBridge.StoreAndForward/ZB.MOM.WW.ScadaBridge.StoreAndForward.csproj

@@ -17,6 +17,7 @@
 
   <ItemGroup>
     <ProjectReference Include="../ZB.MOM.WW.ScadaBridge.Commons/ZB.MOM.WW.ScadaBridge.Commons.csproj" />
+    <ProjectReference Include="../ZB.MOM.WW.ScadaBridge.SiteEventLogging/ZB.MOM.WW.ScadaBridge.SiteEventLogging.csproj" />
   </ItemGroup>
 
   <ItemGroup>