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:**

docs/email-layout-mockup.md

@@ -0,0 +1,26 @@
+# Unified Email Layout – ASCII Mockup
+
+All transactional emails (join confirmation, user confirmation, password reset) use the same layout.
+
+```
++------------------------------------------------------------------+
+|  [Logo or app name – e.g. "Mila" or club name]                   |
++------------------------------------------------------------------+
+|                                                                  |
+|  [Subject / heading line – e.g. "Confirm your email address"]   |
+|                                                                  |
+|  [Body content – paragraph and CTA link]                         |
+|  e.g. "Please click the link below to confirm your request."    |
+|       "Confirm my request" (button or link)                      |
+|                                                                  |
+|  [Optional: short note – e.g. "If you didn't request this,       |
+|   you can ignore this email."]                                   |
+|                                                                  |
++------------------------------------------------------------------+
+|  [Footer – one line, e.g. "© 2025 Mila · Mitgliederverwaltung"]  |
++------------------------------------------------------------------+
+```
+
+- **Header:** Single line (app/club name), subtle.
+- **Main:** Heading + body text + primary CTA (link/button).
+- **Footer:** Single line, small text (copyright / product name).