Fix pads section leaking into llms.txt synopsis, bump to 1.2.7

Ensure double newline separation between @moduledoc and appended pads
documentation so ex_doc synopsis extraction stops before ## Pads.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

Author: FelonEkonom

lib/membrane/core/child.ex

@@ -37,7 +37,7 @@ defmodule Membrane.Core.Child do
         |> Enum.filter(& &1)
         |> Enum.reduce(moduledoc, fn doc, moduledoc ->
           quote do
-            unquote(moduledoc) <> unquote(doc)
+            unquote(moduledoc) <> "\n" <> unquote(doc)
           end
         end)
 

mix.exs

@@ -1,7 +1,7 @@
 defmodule Membrane.Mixfile do
   use Mix.Project
 
-  @version "1.2.6"
+  @version "1.2.7"
   @source_ref "v#{@version}"
   @hex_packages_path "scripts/elixir/hex_packages.exs"