feat(ui): add Node column + filter to AuditLog grid

src/ScadaLink.CentralUI/Components/Audit/AuditFilterBar.razor

@@ -1,8 +1,10 @@
+@using ScadaLink.CentralUI.Services
 @using ScadaLink.Commons.Entities.Sites
 @using ScadaLink.Commons.Interfaces.Repositories
 @using ScadaLink.Commons.Types.Audit
 @using ScadaLink.Commons.Types.Enums
 @inject ISiteRepository SiteRepository
+@inject IAuditLogQueryService AuditLogQueryService
 
 <div class="card mb-3" data-test="audit-filter-bar">
     <div class="card-body py-2">
@@ -58,6 +60,21 @@
                 </div>
             </div>
 
+            @* Node multi-select. Options are the distinct SourceNode values
+               observed in the AuditLog table; the service-side lookup is cached
+               for 60s so a render of this bar costs at most one DB hit per
+               minute per circuit. *@
+            <div class="col-auto" data-test="filter-node">
+                <label class="form-label small mb-1">Node</label>
+                <div>
+                    <MultiSelectDropdown TValue="string"
+                                         Items="_sourceNodes"
+                                         Selected="_model.SourceNodes"
+                                         EmptyText="No nodes available"
+                                         DataTest="filter-node-ms" />
+                </div>
+            </div>
+
             <div class="col-auto" data-test="filter-time-range">
                 <label class="form-label small mb-1" for="audit-time-range">Time range</label>
                 <select id="audit-time-range" class="form-select form-select-sm"

src/ScadaLink.CentralUI/Components/Audit/AuditFilterBar.razor.cs

@@ -31,6 +31,15 @@ public partial class AuditFilterBar
     /// <summary>Site identifiers in display order; rebuilt once when sites load.</summary>
     private IReadOnlyList<string> _siteIds = Array.Empty<string>();
 
+    /// <summary>
+    /// Distinct <c>SourceNode</c> identifiers in display order; populated once
+    /// when the filter bar initialises from the cached
+    /// <see cref="ScadaLink.CentralUI.Services.IAuditLogQueryService.GetDistinctSourceNodesAsync"/>
+    /// snapshot (60s TTL). Failure is non-fatal — the dropdown falls back to
+    /// "No nodes available", mirroring the site loader.
+    /// </summary>
+    private IReadOnlyList<string> _sourceNodes = Array.Empty<string>();
+
     /// <summary>
     /// Raised when the user clicks Apply. Carries the
     /// <see cref="AuditLogQueryFilter"/> the parent page hands to
@@ -80,6 +89,20 @@ public partial class AuditFilterBar
         }
 
         _siteIds = _sites.Select(s => s.SiteIdentifier).ToArray();
+
+        // Populate the Node dropdown alongside the Site dropdown. The service
+        // caches the distinct-nodes lookup for 60s so this never costs more
+        // than one DB hit per minute per circuit; on failure the dropdown
+        // degrades to "No nodes available" like the site loader.
+        try
+        {
+            var nodes = await AuditLogQueryService.GetDistinctSourceNodesAsync();
+            _sourceNodes = nodes.ToArray();
+        }
+        catch
+        {
+            _sourceNodes = Array.Empty<string>();
+        }
     }
 
     /// <summary>
@@ -128,6 +151,7 @@ public partial class AuditFilterBar
         _model.Kinds.Clear();
         _model.Statuses.Clear();
         _model.SiteIdentifiers.Clear();
+        _model.SourceNodes.Clear();
         _model.TimeRange = AuditTimeRangePreset.LastHour;
         _model.CustomFromUtc = null;
         _model.CustomToUtc = null;

src/ScadaLink.CentralUI/Components/Audit/AuditQueryModel.cs

@@ -38,6 +38,14 @@ public sealed class AuditQueryModel
     public HashSet<AuditStatus> Statuses { get; } = new();
     public HashSet<string> SiteIdentifiers { get; } = new(StringComparer.OrdinalIgnoreCase);
 
+    /// <summary>
+    /// Selected source-node identifiers (e.g. <c>"central-a"</c>,
+    /// <c>"site-plant-a-node-a"</c>). Mirrors <see cref="SiteIdentifiers"/> —
+    /// chip multi-select state, empty = "do not constrain", mapped through to
+    /// <see cref="AuditLogQueryFilter.SourceNodes"/> by <see cref="ToFilter"/>.
+    /// </summary>
+    public HashSet<string> SourceNodes { get; } = new(StringComparer.OrdinalIgnoreCase);
+
     public AuditTimeRangePreset TimeRange { get; set; } = AuditTimeRangePreset.LastHour;
     public DateTime? CustomFromUtc { get; set; }
     public DateTime? CustomToUtc { get; set; }
@@ -153,7 +161,8 @@ public sealed class AuditQueryModel
             ExecutionId: executionId,
             ParentExecutionId: parentExecutionId,
             FromUtc: fromUtc,
-            ToUtc: toUtc);
+            ToUtc: toUtc,
+            SourceNodes: SourceNodes.Count > 0 ? SourceNodes.ToArray() : null);
     }
 
     /// <summary>The non-success statuses targeted by the Errors-only toggle.</summary>

src/ScadaLink.CentralUI/Components/Audit/AuditResultsGrid.razor

@@ -105,6 +105,9 @@
             case "Site":
                 <span class="small">@(row.SourceSiteId ?? "—")</span>
                 break;
+            case "Node":
+                <span class="small">@(row.SourceNode ?? "—")</span>
+                break;
             case "Channel":
                 <span class="small">@row.Channel</span>
                 break;

src/ScadaLink.CentralUI/Components/Audit/AuditResultsGrid.razor.cs

@@ -118,6 +118,7 @@ public partial class AuditResultsGrid : IAsyncDisposable
     {
         ("OccurredAtUtc", "OccurredAtUtc"),
         ("Site", "Site"),
+        ("Node", "Node"),
         ("Channel", "Channel"),
         ("Kind", "Kind"),
         ("Status", "Status"),