fix(api-surface): close Theme 9 — 27 naming / dead-code / config / hygiene findings

The largest themed batch — small mechanical fixes across 11 modules.

API / message hygiene:
- Comm-020: SiteAddressCacheLoaded now carries IReadOnlyDictionary /
  IReadOnlyList — Akka messages must be immutable.
- Commons-016: BundleSession.MaxUnlockAttempts named constant replaces
  magic 3.
- Commons-018: IOperationTrackingStore + IPartitionMaintenance moved from
  Interfaces/ root to Interfaces/Services/ (namespace preserved — 9
  consumers exceeded the in-prompt move threshold).
- Commons-023: TrackingStatusSnapshot.SourceNode now consistent with the
  trailing-optional-with-default pattern used elsewhere.
- SR-022: AuditingDbCommand.DbConnection.set no longer uses reflection —
  exposes AuditingDbConnection.Inner via internal API surface.

Dead code / config cleanup:
- ClusterInfra-011: decorative SectionName constant deleted.
- ClusterInfra-014: dead AddClusterInfrastructureActors method + its
  "throws-when-called" test deleted.
- Host-021: Microsoft Logging:LogLevel block deleted from appsettings.json
  (dead under Serilog).

Fail-loud over fail-silent:
- DM-021: ResolveSiteIdentifierAsync throws on missing site (was silently
  substituting a DB id).
- DM-022: dropped transient Pending write — record now lands directly in
  InProgress (no UI flicker, one fewer DB write).
- Host-020: LoggerConfigurationFactory emits a Console.Error warning when
  both Serilog:MinimumLevel and ScadaLink:Logging:MinimumLevel are set
  (ScadaLink remains truth per Host-011).
- SnF-022: NotifyCachedCallObserverAsync logs Warning on unparseable
  TrackedOperationId (was silently dropping).
- SnF-023: empty siteId default replaced with $unknown-site sentinel
  + constructor normalisation.

Correctness:
- SCA-001: SupervisorStrategy XML rewritten to match actual
  DefaultDecider/Restart semantics (was claiming Resume).
- SCA-003: OnUpsertAsync now restamps IngestedAtUtc on every upsert.
- SR-021: HandleDeployArtifacts now dispatches an internal
  ApplyArtifactDataConnectionsToDcl message after the SQLite write so
  system-wide artifact-deploy data-connection changes go live
  immediately (was requiring a site restart).
- SnF-020: RetryParkedMessageAsync captures the parked row BEFORE the
  local write so a concurrent delete can't skip standby replication.

Sentinels / naming collisions:
- HM-021: CentralSiteId changed from "central" to "$central"
  (uncollideable — leading $ is forbidden in real SiteIdentifiers).

Doc / surface cleanups:
- SEL-018: FailedWriteCount promoted to ISiteEventLogger; XML softened
  to "Available for future Health Monitoring integration".
- SnF-019: VERIFY outcome — documented parking-after-DefaultMaxRetries
  in Component-StoreAndForward.md + DefaultMaxRetries XML (uniform
  cap; maxRetries:0 is the unbounded escape hatch).
- SnF-021: Component-StoreAndForward.md no longer claims the tracking
  table lives in SnF — it's in SiteRuntime, the interface is in Commons.
- CLI-020: bundle export response parse guarded with try/catch on
  JsonException / KeyNotFoundException / FormatException — emits a
  clean INVALID_RESPONSE exit instead of a stack trace.

Config:
- ClusterInfra-013: intent comment added to "catastrophic config" test.
- Host-016: appsettings.Site.json second CentralContactPoints entry
  removed (was pointing at the SITE's own port); doc-key explains how
  to extend.
- Host-018: NodeName added to both shipped per-role configs (was
  causing SourceNode to be null on audit rows).

UI:
- CentralUI-029: replaced JS.InvokeAsync<int>("eval", …) with an ES
  module import (new wwwroot/js/browser-time.js).
- CentralUI-032: AuditResultsGrid gains a Previous button backed by a
  cursor stack.

10+ new regression tests across the affected projects. Build clean;
all suites green. README regenerated: 6 open (was 33).

Session-to-date: 130 of 136 originally-open Theme findings closed.

src/ScadaLink.Communication/Actors/CentralCommunicationActor.cs

@@ -410,7 +410,14 @@ public class CentralCommunicationActor : ReceiveActor
                     contacts[site.SiteIdentifier] = addrs;
             }
 
-            return new SiteAddressCacheLoaded(contacts);
+            // Communication-020: freeze the cross-task payload before piping to
+            // Self. The message record exposes read-only types (
+            // IReadOnlyDictionary / IReadOnlyList) so the Akka.NET message-
+            // immutability convention is enforced by type, not just convention.
+            var frozen = contacts.ToDictionary(
+                kvp => kvp.Key,
+                kvp => (IReadOnlyList<string>)kvp.Value.AsReadOnly());
+            return new SiteAddressCacheLoaded(frozen);
         }).PipeTo(self);
     }
 
@@ -540,8 +547,14 @@ public record RefreshSiteAddresses;
 /// <summary>
 /// Internal message carrying the loaded site contact data from the database.
 /// ClusterClient creation happens on the actor thread in HandleSiteAddressCacheLoaded.
+///
+/// Communication-020: the payload is exposed as <see cref="IReadOnlyDictionary{TKey,TValue}"/>
+/// of <see cref="IReadOnlyList{T}"/> so the Akka.NET "messages are immutable"
+/// convention is enforced at the type level rather than relying on producer
+/// discipline. The producer wraps the constructed buckets with
+/// <c>List&lt;T&gt;.AsReadOnly()</c> before piping to Self.
 /// </summary>
-internal record SiteAddressCacheLoaded(Dictionary<string, List<string>> SiteContacts);
+internal record SiteAddressCacheLoaded(IReadOnlyDictionary<string, IReadOnlyList<string>> SiteContacts);
 
 /// <summary>
 /// Notification sent to debug view subscribers when the stream is terminated