feat(audit): M5.5 per-channel retention overrides via purge-role bounded delete (T3)

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

@@ -28,6 +28,24 @@ public sealed class AuditLogPurgeOptions
     /// <summary>Period of the purge tick in hours (default 24).</summary>
     public int IntervalHours { get; set; } = 24;
 
+    /// <summary>
+    /// M5.5 (T3): batch size for the per-channel retention-override row DELETE
+    /// (<see cref="ZB.MOM.WW.ScadaBridge.Commons.Interfaces.Repositories.IAuditLogRepository.PurgeChannelOlderThanAsync"/>).
+    /// Each <c>DELETE TOP (@batch)</c> caps the transaction-log and lock footprint
+    /// per statement; the repository loops batches until no rows remain. Default
+    /// 5000 keeps individual deletes short on a busy central DB while still draining
+    /// a large backlog within a tick. Clamped to a sane minimum in
+    /// <see cref="ChannelPurgeBatchSize"/>.
+    /// </summary>
+    public int ChannelPurgeBatchSizeConfigured { get; set; } = 5000;
+
+    /// <summary>
+    /// Resolves the effective per-channel purge batch size, clamped to at least 1 so
+    /// a misconfigured <c>0</c>/negative value cannot make the repository's DELETE
+    /// loop spin or throw.
+    /// </summary>
+    public int ChannelPurgeBatchSize => ChannelPurgeBatchSizeConfigured < 1 ? 1 : ChannelPurgeBatchSizeConfigured;
+
     /// <summary>
     /// Test-only override for finer control over the tick cadence than
     /// whole-hour resolution allows. When non-null, takes precedence over