feat: add join confirmation and mail templating

lib/mv/mailer.ex

@@ -1,3 +1,19 @@
 defmodule Mv.Mailer do
+  @moduledoc """
+  Swoosh mailer for transactional emails.
+
+  Use `mail_from/0` for the configured sender address (join confirmation,
+  user confirmation, password reset).
+  """
   use Swoosh.Mailer, otp_app: :mv
+
+  @doc """
+  Returns the configured "from" address for transactional emails.
+
+  Configure in config.exs or runtime.exs as `config :mv, :mail_from, {name, email}`.
+  Default: `{"Mila", "noreply@example.com"}`.
+  """
+  def mail_from do
+    Application.get_env(:mv, :mail_from, {"Mila", "noreply@example.com"})
+  end
 end