Fix Forgejo IONOS SMTP: STARTTLS on smtp.ionos.de

Use PROTOCOL=smtp+starttls with the EU relay (smtp.ionos.de). Port 587 with
implicit TLS on smtp.ionos.com failed TLS handshake; .com auth also fails for
EU mailboxes. Document OpenBao PASSWD field mapping in operator docs.

helm/forgejo-values.yaml

@@ -59,9 +59,10 @@ gitea:
     mailer:
       ENABLED: true
       FROM: forgejo@coulomb.social
-      MAILER_TYPE: smtp
-      HOST: smtp.ionos.com:587
-      IS_TLS_ENABLED: true
+      # IONOS submission port 587 uses STARTTLS, not implicit TLS (smtps).
+      PROTOCOL: smtp+starttls
+      SMTP_ADDR: smtp.ionos.de
+      SMTP_PORT: 587
       USER: forgejo@coulomb.social
     actions:
       ENABLED: true