feat(ui/deployment): consolidate sites/areas/instances into Topology page

Single /deployment/topology page replaces /deployment/instances (legacy URL
preserved as a secondary @page directive) and the /admin/areas* CRUD pages.
TreeView with Site → Area → Instance, V1–V7 visual guide (bi-building /
bi-diagram-3 / bi-box), always-visible empty containers, search dim, F2
inline area rename, and right-click context menus per node kind (Add Area,
Move to Area…, lifecycle actions, etc.).

Adds AreaService.MoveAreaAsync with cycle prevention, same-site enforcement,
and name-collision check at the new parent. Instance rename intentionally
out of scope — UniqueName is the site-side actor identity, requires its own
design pass.

src/ScadaLink.TemplateEngine/Services/AreaService.cs

@@ -96,6 +96,61 @@ public class AreaService
         return Result<Area>.Success(area);
     }
 
+    /// <summary>
+    /// Re-parents an area within its site. `newParentAreaId == null` moves the area to the site root.
+    /// Rejects: self-parent, descendant-parent (cycle), cross-site parent, name collision at new level.
+    /// </summary>
+    public async Task<Result<Area>> MoveAreaAsync(
+        int areaId, int? newParentAreaId, string user,
+        CancellationToken cancellationToken = default)
+    {
+        var area = await _repository.GetAreaByIdAsync(areaId, cancellationToken);
+        if (area == null)
+            return Result<Area>.Failure($"Area with ID {areaId} not found.");
+
+        if (newParentAreaId == areaId)
+            return Result<Area>.Failure("An area cannot be its own parent.");
+
+        if (newParentAreaId.HasValue)
+        {
+            var newParent = await _repository.GetAreaByIdAsync(newParentAreaId.Value, cancellationToken);
+            if (newParent == null)
+                return Result<Area>.Failure($"Target parent area with ID {newParentAreaId.Value} not found.");
+            if (newParent.SiteId != area.SiteId)
+                return Result<Area>.Failure("Areas can only be moved within the same site.");
+        }
+
+        var siblings = await _repository.GetAreasBySiteIdAsync(area.SiteId, cancellationToken);
+
+        // Cycle prevention: the new parent must not be a descendant of the area being moved.
+        if (newParentAreaId.HasValue)
+        {
+            var descendants = GetDescendantAreaIds(areaId, siblings);
+            if (descendants.Contains(newParentAreaId.Value))
+                return Result<Area>.Failure(
+                    $"Cannot move area '{area.Name}' under one of its own descendants.");
+        }
+
+        if (newParentAreaId == area.ParentAreaId)
+            return Result<Area>.Success(area);
+
+        var collision = siblings.FirstOrDefault(a =>
+            a.Id != areaId &&
+            a.ParentAreaId == newParentAreaId &&
+            string.Equals(a.Name, area.Name, StringComparison.OrdinalIgnoreCase));
+        if (collision != null)
+            return Result<Area>.Failure(
+                $"An area named '{area.Name}' already exists at the target level.");
+
+        area.ParentAreaId = newParentAreaId;
+        await _repository.UpdateAreaAsync(area, cancellationToken);
+        await _repository.SaveChangesAsync(cancellationToken);
+
+        await _auditService.LogAsync(user, "Move", "Area", area.Id.ToString(), area.Name, area, cancellationToken);
+
+        return Result<Area>.Success(area);
+    }
+
     /// <summary>
     /// Deletes an area. Blocked if instances are assigned to this area or any descendant area.
     /// </summary>