fix(options): bind + validate OperationTrackingOptions; register the site IOperationTrackingStore that two comments claimed AddSiteRuntime provides (plan R2-08 T8, arch-review 08r2 NF4)

VERIFY-THEN-FIX: the plan-authoring discovery is CONFIRMED. No code anywhere in
src/ registered IOperationTrackingStore in DI, yet AkkaHostedService and
AuditLog SCE both comment that AddSiteRuntime provides it. Every consumer
resolved it via GetService (null-tolerant) and silently ran degraded:
cached-drain scheduler never armed, PullSiteCalls reconciliation seam never
wired, Tracking.Status degraded to audit-only. This is a FUNCTIONAL FIX riding
the hygiene plan: AddSiteRuntime now registers the store (site-only), so
site-local cached-call tracking runs in its intended mode. OperationTrackingOptions
is now bound + eagerly validated in the Host site-options block.

src/ZB.MOM.WW.ScadaBridge.SiteRuntime/Tracking/OperationTrackingOptionsValidator.cs

@@ -0,0 +1,26 @@
+using ZB.MOM.WW.Configuration;
+
+namespace ZB.MOM.WW.ScadaBridge.SiteRuntime.Tracking;
+
+/// <summary>
+/// Validates <see cref="OperationTrackingOptions"/> at host startup (arch-review
+/// 08 round 2 NF4). <see cref="OperationTrackingStore"/> opens the SQLite
+/// connection string in its constructor, so an empty/blank connection string
+/// must fail the host at boot rather than throw opaquely on first resolve. The
+/// retention window must be positive — a zero would make the host's terminal-row
+/// purge delete every tracking row.
+/// </summary>
+public sealed class OperationTrackingOptionsValidator : OptionsValidatorBase<OperationTrackingOptions>
+{
+    /// <inheritdoc />
+    protected override void Validate(ValidationBuilder builder, OperationTrackingOptions options)
+    {
+        builder.RequireThat(!string.IsNullOrWhiteSpace(options.ConnectionString),
+            $"ScadaBridge:OperationTracking:{nameof(OperationTrackingOptions.ConnectionString)} " +
+            "must be a non-empty SQLite connection string.");
+
+        builder.RequireThat(options.RetentionDays > 0,
+            $"ScadaBridge:OperationTracking:{nameof(OperationTrackingOptions.RetentionDays)} " +
+            $"({options.RetentionDays}) must be > 0.");
+    }
+}