feat(m9/T24a): guarded move-data-connection-between-sites command + handler

src/ZB.MOM.WW.ScadaBridge.Commons/Interfaces/Repositories/ISiteRepository.cs

@@ -70,13 +70,26 @@ public interface ISiteRepository
     /// <returns>A task that represents the asynchronous operation.</returns>
     Task DeleteDataConnectionAsync(int id, CancellationToken cancellationToken = default);
 
-    // Instances (for deletion constraint checks)
+    // Instances (for deletion / move constraint checks)
     /// <summary>Retrieves all instances deployed to a site.</summary>
     /// <param name="siteId">The site primary key to filter by.</param>
     /// <param name="cancellationToken">Cancellation token.</param>
     /// <returns>A task that resolves to a read-only list of <see cref="Instance"/> entities for the given site.</returns>
     Task<IReadOnlyList<Instance>> GetInstancesBySiteIdAsync(int siteId, CancellationToken cancellationToken = default);
 
+    /// <summary>
+    /// Retrieves the distinct instances that have at least one
+    /// <see cref="InstanceConnectionBinding"/> referencing the given data
+    /// connection. Used as the primary data-integrity guard for moving a
+    /// connection between sites: a bound connection cannot leave its site
+    /// without orphaning the (site-scoped) binding, so the move handler rejects
+    /// the move and names the returned instances as blockers.
+    /// </summary>
+    /// <param name="dataConnectionId">The data connection primary key.</param>
+    /// <param name="cancellationToken">Cancellation token.</param>
+    /// <returns>A task that resolves to the distinct referencing <see cref="Instance"/> entities (empty when none).</returns>
+    Task<IReadOnlyList<Instance>> GetInstancesReferencingDataConnectionAsync(int dataConnectionId, CancellationToken cancellationToken = default);
+
     /// <summary>Saves all pending changes to the database.</summary>
     /// <param name="cancellationToken">Cancellation token.</param>
     /// <returns>A task that resolves to the number of state entries written to the database.</returns>