feat: add join confirmation and mail templating

lib/mv_web/emails/email_layout_view.ex

@@ -0,0 +1,12 @@
+defmodule MvWeb.EmailLayoutView do
+  @moduledoc """
+  Layout view for transactional emails (join confirmation, user confirmation, password reset).
+
+  Renders a single layout template that wraps all email body content.
+  See docs/email-layout-mockup.md for the layout structure.
+  """
+  use Phoenix.View,
+    root: "lib/mv_web",
+    path: "templates/emails/layouts",
+    namespace: MvWeb
+end