fix(deployment): instance delete fully removes the record

Deleting an instance only undeployed it from the site and set the state
to NotDeployed, leaving an orphan record that could never be removed —
the state-transition matrix rejected delete from NotDeployed.

Delete now removes the instance record entirely (deployment history,
snapshot, attribute/alarm overrides, and connection bindings go with
it), and is permitted from any state.

src/ScadaLink.Commons/Interfaces/Repositories/IDeploymentManagerRepository.cs

@@ -34,5 +34,12 @@ public interface IDeploymentManagerRepository
     Task<Instance?> GetInstanceByUniqueNameAsync(string uniqueName, CancellationToken cancellationToken = default);
     Task UpdateInstanceAsync(Instance instance, CancellationToken cancellationToken = default);
 
+    /// <summary>
+    /// Removes an instance and everything that depends on it: deployment
+    /// records, deployed config snapshot, attribute/alarm overrides, and
+    /// connection bindings.
+    /// </summary>
+    Task DeleteInstanceAsync(int instanceId, CancellationToken cancellationToken = default);
+
     Task<int> SaveChangesAsync(CancellationToken cancellationToken = default);
 }