feat(db): add SourceNode column + IX_AuditLog_Node_Occurred index to AuditLog

src/ScadaLink.ConfigurationDatabase/Configurations/AuditLogEntityTypeConfiguration.cs

@@ -70,6 +70,14 @@ public class AuditLogEntityTypeConfiguration : IEntityTypeConfiguration<AuditEve
             .HasMaxLength(256)
             .IsUnicode(false);
 
+        // SourceNode (Audit Log #23, SourceNode-stamping): node-local identifier of the
+        // cluster member that produced the row (e.g. "node-a", "central-a"). NULL is
+        // valid for reconciled rows from a retired node and for direct-write rows
+        // produced before this feature shipped. ASCII — varchar(64), no unicode.
+        builder.Property(e => e.SourceNode)
+            .HasColumnType("varchar(64)")
+            .HasMaxLength(64);
+
         // Bounded unicode message column.
         builder.Property(e => e.ErrorMessage)
             .HasMaxLength(1024);
@@ -97,6 +105,14 @@ public class AuditLogEntityTypeConfiguration : IEntityTypeConfiguration<AuditEve
             .HasFilter("[ParentExecutionId] IS NOT NULL")
             .HasDatabaseName("IX_AuditLog_ParentExecution");
 
+        // SourceNode composite index (Audit Log #23, SourceNode-stamping): backs
+        // per-node Central UI / health-dashboard queries (e.g. "rows produced by
+        // central-a, newest first"). Created via raw SQL in the migration so it lands
+        // on the ps_AuditLog_Month(OccurredAtUtc) partition scheme like every other
+        // IX_AuditLog_* index — keeps the partition-switch purge path intact.
+        builder.HasIndex(e => new { e.SourceNode, e.OccurredAtUtc })
+            .HasDatabaseName("IX_AuditLog_Node_Occurred");
+
         builder.HasIndex(e => new { e.Channel, e.Status, e.OccurredAtUtc })
             .IsDescending(false, false, true)
             .HasDatabaseName("IX_AuditLog_Channel_Status_Occurred");

src/ScadaLink.ConfigurationDatabase/Configurations/NotificationOutboxConfiguration.cs

@@ -47,6 +47,11 @@ public class NotificationOutboxConfiguration : IEntityTypeConfiguration<Notifica
 
         builder.Property(n => n.SourceScript).HasMaxLength(200);
 
+        // SourceNode (Audit Log #23, SourceNode-stamping): mapped in a follow-on migration
+        // (AddNotificationSourceNode). Ignored here for now so the AddAuditLogSourceNode
+        // migration only touches AuditLog. Removed in the AddNotificationSourceNode commit.
+        builder.Ignore(n => n.SourceNode);
+
         // OriginExecutionId (Audit Log #23): nullable uniqueidentifier carried from the
         // site so the dispatcher can echo it onto NotifyDeliver audit rows. No index —
         // it is never a query predicate on this table, only copied onto audit events.

src/ScadaLink.ConfigurationDatabase/Configurations/SiteCallEntityTypeConfiguration.cs

@@ -59,6 +59,11 @@ public class SiteCallEntityTypeConfiguration : IEntityTypeConfiguration<SiteCall
         builder.Property(s => s.LastError)
             .HasMaxLength(1024);
 
+        // SourceNode (Audit Log #23, SourceNode-stamping): mapped in a follow-on migration
+        // (AddSiteCallSourceNode). Ignored here for now so the AddAuditLogSourceNode
+        // migration only touches AuditLog. Removed in the AddSiteCallSourceNode commit.
+        builder.Ignore(s => s.SourceNode);
+
         // Indexes — names locked for reconciliation/migration discoverability.
         // Source_Created backs "calls from this site" (Central UI Site Calls page,
         // filter by SourceSite, newest first).