feat: category filter includes subcategories

lib/components_elixir/inventory/hierarchical.ex

@@ -143,6 +143,32 @@ defmodule ComponentsElixir.Inventory.Hierarchical do
     end)
   end
 
+  @doc """
+  Gets all descendant IDs for a given entity ID, including the entity itself.
+  This recursively finds all children, grandchildren, etc.
+
+  ## Examples
+      iex> categories = [
+      ...>   %{id: 1, parent_id: nil},
+      ...>   %{id: 2, parent_id: 1},
+      ...>   %{id: 3, parent_id: 2},
+      ...>   %{id: 4, parent_id: 1}
+      ...> ]
+      iex> Hierarchical.descendant_ids(categories, 1, &(&1.parent_id))
+      [1, 2, 3, 4]
+  """
+  def descendant_ids(entities, entity_id, parent_id_accessor_fn) do
+    [entity_id | get_descendant_ids_recursive(entities, entity_id, parent_id_accessor_fn)]
+  end
+
+  defp get_descendant_ids_recursive(entities, parent_id, parent_id_accessor_fn) do
+    children = child_entities(entities, parent_id, parent_id_accessor_fn)
+
+    Enum.flat_map(children, fn child ->
+      [child.id | get_descendant_ids_recursive(entities, child.id, parent_id_accessor_fn)]
+    end)
+  end
+
   @doc """
   Generates display name for entity including parent context.
   For dropdown displays: "Parent > Child"