perf(sitelog): sampled per-run events; interval run summaries; site_events replication policy pinned

Implements WP3.2 stage (b) per docs/plans/2026-08-15-site-events-policy-design.md.

- Per-run instance-script Started/Completed Info site events are now off by
  default (SiteRuntimeOptions.PerRunScriptEvents=false) instead of firing on
  every run, closing the dominant site_events writer. Gated at the ScriptRunLauncher
  call sites (moved there from ScriptExecutionActor by WP3.1). Error-level events
  (timeout/failure/stuck-watchdog/recursion-limit) remain unconditional.
- ScriptRunSummaryRecorder accumulates per-(instance, script) run counters and a
  new site-only ScriptRunSummaryFlushService emits one aggregate "script" Info
  site event per ScriptRunSummaryIntervalSeconds (default 300s), top-50-script
  breakdown with an "others" rollup, zero-activity intervals emit nothing.
- Per-script opt-in via PerRunScriptEventScripts ("Instance/Script" exact or
  "Instance/*" wildcard), matched by the new pure ScriptRunEventPolicy. All three
  options are read from IOptionsMonitor<SiteRuntimeOptions> per run, so the
  policy is hot-togglable without a restart.
- Fixed the stale "event log is not replicated" comment at AkkaHostedService.cs
  (~905): site_events IS registered in SiteLocalDbSetup.ReplicatedTables — the
  singleton is what makes queries always hit the actively-written copy;
  replication is what gives the singleton history to read after a failover
  (memo Decision (b)). site_events replication itself is unchanged (still
  registered) and already pinned by
  tests/ZB.MOM.WW.ScadaBridge.Host.Tests/SiteLocalDbCdcRegistrationTests.cs.
- Updated Component-SiteEventLogging.md (Volume Policy section, corrected
  Storage/replication rationale) and Component-SiteRuntime.md (Script Run
  Launch + Error Handling sections).

src/ZB.MOM.WW.ScadaBridge.SiteRuntime/ServiceCollectionExtensions.cs

@@ -4,6 +4,7 @@ using Microsoft.Extensions.Options;
 using ZB.MOM.WW.LocalDb;
 using ZB.MOM.WW.ScadaBridge.Communication.Grpc;
 using ZB.MOM.WW.ScadaBridge.Commons.Interfaces.Repositories;
+using ZB.MOM.WW.ScadaBridge.SiteEventLogging;
 using ZB.MOM.WW.ScadaBridge.SiteRuntime.Deployment;
 using ZB.MOM.WW.ScadaBridge.SiteRuntime.Persistence;
 using ZB.MOM.WW.ScadaBridge.SiteRuntime.Repositories;
@@ -98,6 +99,18 @@ public static class ServiceCollectionExtensions
             sp.GetRequiredService<SiteStreamManager>(),
             sp.GetRequiredService<ILogger<Streaming.SiteStreamAlarmDropReporter>>()));
 
+        // WP3.2 (site_events volume policy): the recorder is a singleton so ScriptRunLauncher
+        // can resolve it from the root service provider on every run, the same way it already
+        // resolves ISiteEventLogger. The flush service is registered ONLY here — central
+        // composition roots never call AddSiteRuntime(), which is what makes the periodic
+        // "script" summary event site-only, matching the design memo.
+        services.AddSingleton<ScriptRunSummaryRecorder>();
+        services.AddHostedService(sp => new ScriptRunSummaryFlushService(
+            sp.GetRequiredService<ScriptRunSummaryRecorder>(),
+            sp.GetRequiredService<ISiteEventLogger>(),
+            sp.GetRequiredService<IOptionsMonitor<SiteRuntimeOptions>>(),
+            sp.GetRequiredService<ILogger<ScriptRunSummaryFlushService>>()));
+
         return services;
     }