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/SiteRuntimeOptionsValidator.cs

@@ -86,5 +86,10 @@ public sealed class SiteRuntimeOptionsValidator : OptionsValidatorBase<SiteRunti
         builder.RequireThat(options.AlarmPublishQueueCapacity > 0,
             $"ScadaBridge:SiteRuntime:AlarmPublishQueueCapacity must be greater than 0 " +
             $"(was {options.AlarmPublishQueueCapacity}); it bounds SiteStreamManager's dedicated alarm publish queue.");
+
+        builder.RequireThat(options.ScriptRunSummaryIntervalSeconds >= 0,
+            $"ScadaBridge:SiteRuntime:ScriptRunSummaryIntervalSeconds must be >= 0 " +
+            $"(was {options.ScriptRunSummaryIntervalSeconds}); it is the ScriptRunSummaryRecorder " +
+            "flush interval and a negative value throws inside its delay. 0 disables the flush.");
     }
 }