feat(mail): outbox, SMTP sender and config

readme.md

@@ -148,6 +148,9 @@ the login module writes "view as" to the audit table through `shared/audit/Admin
 use each other.
 `hint` (dashboard hints and their admin API) uses `JdbcTemplate` in a `repo` package too, and audits through
 `shared/audit/AdminAuditLog`.
+`mail` writes each mail as a finished text into `mail_outbox` (`JdbcTemplate`, `repo`), in the transaction of the
+event, and `MailOutboxService` sends the rows every minute over SMTP. Other modules reach it through the port
+`shared/mail/AccountMailer`. Without `SPRING_MAIL_HOST` mail is off: the rows wait and go out once a host is set.
 
 ArchUnit enforces these rules in `src/test/java/auth_service/architecture/ArchitectureTest.java`, so a layer
 violation fails the build. It also keeps the modules independent of each other and free of cycles. Test base
@@ -303,6 +306,9 @@ Configuration comes from environment variables:
 | `APP_PUBLIC_URL` | Auth's public address, the Steam OpenID realm (default `http://localhost:8080`) |
 | `APP_FRONTEND_URL` | Where the Steam link ends (default `http://localhost:5173`) |
 | `APP_CORE_INTERNAL_URL` | Core for the nightly account cleanup, required (local `http://localhost:8090`, Docker `http://tbp-core-service:8090`) |
+| `SPRING_MAIL_HOST`, `SPRING_MAIL_USERNAME`, `SPRING_MAIL_PASSWORD` | SMTP server and its login (port 465, SSL). No host = mail off |
+| `APP_MAIL_FROM` | Sender address, the mailbox of the SMTP login. Needed with a host |
+| `APP_MAIL_ADMIN_TO` | Gets "new user registered". Needed with a host |
 
 Generate a keypair: