Add EnsureEntity<T> method to DbModelOptions

Introduce EnsureEntity<T>(bool isVirtual) to validate and ensure entity options exist for a given type in either Entities or VirtualEntities. Throws an exception if options are missing.

src/ReC.Infrastructure/Options/DbModelOptions.cs

@@ -7,4 +7,17 @@ public record DbModelOptions
     public Dictionary<string, EntityOptions> Entities { get; init; } = [];
 
     public Dictionary<string, VirtualEntityOptions> VirtualEntities { get; init; } = [];
+
+    public void EnsureEntity<T>(bool isVirtual)
+    {
+
+        var cluster = isVirtual
+            ? VirtualEntities.ToDictionary(kvp => kvp.Key, kvp => kvp.Value as EntityBaseOptions)
+            : Entities.ToDictionary(kvp => kvp.Key, kvp => kvp.Value as EntityBaseOptions);
+
+        if(cluster.TryGetValue(nameof(T), out var entityOptions))
+            entityOptions.EnsureProperties<T>();
+        else
+            throw new InvalidOperationException($"Entity options for type '{typeof(T).FullName}' not found.");
+    }
 }