feat: add join confirmation and mail templating

CODE_GUIDELINES.md

@@ -1255,32 +1255,32 @@ mix deps.update phoenix
 mix hex.outdated
 ```
 
-### 3.11 Email: Swoosh
+### 3.11 Email: Swoosh and Phoenix.Swoosh
 
-**Mailer Configuration:**
+**Mailer and from address:**
+
+- `Mv.Mailer` (Swoosh) and `Mv.Mailer.mail_from/0` return the configured sender `{name, email}`.
+- Config: `config :mv, :mail_from, {"Mila", "noreply@example.com"}` in config.exs; override in runtime.exs from ENV for production.
+
+**Unified layout (transactional emails):**
+
+- All transactional emails (join confirmation, user confirmation, password reset) use the same layout: `MvWeb.EmailLayoutView` (layout) and `MvWeb.EmailsView` (body templates).
+- Templates live under `lib/mv_web/templates/emails/` (bodies) and `lib/mv_web/templates/emails/layouts/` (layout). Use Gettext in templates for i18n.
+- See `MvWeb.Emails.JoinConfirmationEmail`, `Mv.Accounts.User.Senders.SendNewUserConfirmationEmail`, `SendPasswordResetEmail` for the pattern; see `docs/email-layout-mockup.md` for layout structure.
+
+**Sending with layout:**
 
 ```elixir
-defmodule Mv.Mailer do
-  use Swoosh.Mailer, otp_app: :mv
-end
-```
+use Phoenix.Swoosh, view: MvWeb.EmailsView, layout: {MvWeb.EmailLayoutView, "layout.html"}
 
-**Sending Emails:**
-
-```elixir
-defmodule Mv.Accounts.WelcomeEmail do
-  use Phoenix.Swoosh, template_root: "lib/mv_web/templates"
-  import Swoosh.Email
-
-  def send(user) do
-    new()
-    |> to({user.name, user.email})
-    |> from({"Mila", "noreply@mila.example.com"})
-    |> subject("Welcome to Mila!")
-    |> render_body("welcome.html", %{user: user})
-    |> Mv.Mailer.deliver()
-  end
-end
+new()
+|> from(Mailer.mail_from())
+|> to(email_address)
+|> subject(gettext("Subject"))
+|> put_view(MvWeb.EmailsView)
+|> put_layout({MvWeb.EmailLayoutView, "layout.html"})
+|> render_body("template_name.html", %{assigns})
+|> Mailer.deliver!()
 ```
 
 ### 3.12 Internationalization: Gettext