feat: add join confirmation and mail templating

docs/development-progress-log.md

@@ -800,6 +800,14 @@ end
 - Domain: `Mv.Membership.submit_join_request/2`, `Mv.Membership.confirm_join_request/2` (token hashing via `JoinRequest.hash_confirmation_token/1`, lookup, expiry check, idempotency for :submitted/:approved/:rejected).
 - Test file: `test/membership/join_request_test.exs` – all tests pass; policy test and expired-token test implemented.
 
+**Subtask 2 – Submit and confirm flow (done):**
+- **Unified email layout:** phoenix_swoosh with `MvWeb.EmailLayoutView` (layout) and `MvWeb.EmailsView` (body templates). All transactional emails (join confirmation, user confirmation, password reset) use the same layout. Config: `config :mv, :mail_from, {name, email}` (default `{"Mila", "noreply@example.com"}`); override in runtime.exs.
+- **Join confirmation:** Domain wrapper `submit_join_request/2` generates token (or uses optional `:confirmation_token` in attrs for tests), creates JoinRequest via action `:submit`, then sends one email via `MvWeb.Emails.JoinConfirmationEmail`. Route `GET /confirm_join/:token` (JoinConfirmController) updates to `submitted`; idempotent; expired/invalid handled.
+- **Senders migrated:** `SendNewUserConfirmationEmail`, `SendPasswordResetEmail` use layout + `Mv.Mailer.mail_from/0`.
+- **Cleanup:** Mix task `mix join_requests.cleanup_expired` hard-deletes JoinRequests in `pending_confirmation` with expired `confirmation_token_expires_at` (authorize?: false). For cron/Oban.
+- **Gettext:** New email strings in default domain; German translations in de/LC_MESSAGES/default.po.
+- Tests: `join_request_test.exs`, `join_request_submit_email_test.exs`, `join_confirm_controller_test.exs` – all pass.
+
 ### Test Data Management
 
 **Seed Data:**