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.ConfigurationDatabase/Repositories/DeploymentManagerRepository.cs

@@ -189,6 +189,27 @@ public class DeploymentManagerRepository : IDeploymentManagerRepository
         return Task.CompletedTask;
     }
 
+    public async Task DeleteInstanceAsync(int instanceId, CancellationToken cancellationToken = default)
+    {
+        // DeploymentRecords have a Restrict FK to Instance — remove them
+        // explicitly first. The snapshot, overrides, and connection bindings
+        // are configured with cascade delete and go with the instance.
+        var records = await _dbContext.DeploymentRecords
+            .Where(d => d.InstanceId == instanceId)
+            .ToListAsync(cancellationToken);
+        if (records.Count > 0)
+        {
+            _dbContext.DeploymentRecords.RemoveRange(records);
+        }
+
+        var instance = await _dbContext.Set<Instance>()
+            .FirstOrDefaultAsync(i => i.Id == instanceId, cancellationToken);
+        if (instance != null)
+        {
+            _dbContext.Set<Instance>().Remove(instance);
+        }
+    }
+
     public async Task<int> SaveChangesAsync(CancellationToken cancellationToken = default)
     {
         return await _dbContext.SaveChangesAsync(cancellationToken);