perf(central): set-based ingest, aligned partition purge, KPI query shapes, EF hygiene

src/ZB.MOM.WW.ScadaBridge.AuditLog/Central/AuditLogPurgeActor.cs

@@ -17,8 +17,9 @@ namespace ZB.MOM.WW.ScadaBridge.AuditLog.Central;
 ///       for monthly boundaries whose latest <c>OccurredAtUtc</c> is older
 ///       than <c>DateTime.UtcNow - RetentionDays</c>.</item>
 /// <item>For each eligible boundary, calls
-///       <see cref="IAuditLogRepository.SwitchOutPartitionAsync"/> which runs
-///       the drop-and-rebuild dance around <c>UX_AuditLog_EventId</c>.</item>
+///       <see cref="IAuditLogRepository.SwitchOutPartitionAsync"/>, a
+///       metadata-only staging-table switch (WP2.2 removed the index
+///       drop/rebuild that used to bracket it).</item>
 /// <item>Publishes <see cref="AuditLogPurgedEvent"/> on the actor-system
 ///       EventStream so the central health collector + ops surfaces
 ///       can subscribe without coupling to this actor.</item>
@@ -26,11 +27,10 @@ namespace ZB.MOM.WW.ScadaBridge.AuditLog.Central;
 /// </summary>
 /// <remarks>
 /// <para>
-/// <b>Daily cadence.</b> Partition switch is metadata-only but the
-/// drop-and-rebuild dance briefly removes <c>UX_AuditLog_EventId</c>; running
-/// more often than necessary trades unique-index rebuild outages for
-/// negligible freshness wins. The default 24-hour interval matches
-/// alog.md §10's retention policy.
+/// <b>Daily cadence.</b> The partition switch is metadata-only, but it still
+/// takes schema-modification locks on a table the ingest path is writing to;
+/// running more often than necessary trades contention for negligible freshness
+/// wins. The default 24-hour interval matches alog.md §10's retention policy.
 /// </para>
 /// <para>
 /// <b>Continue-on-error.</b> A single boundary that throws (transient SQL