Fix the mail scheme example — smtp and smtps, not tls

Symfony's mailer only knows the schemes smtp and smtps; the example's
MAIL_SCHEME=tls (and the "tls | smtps (465)" comment naming it as an
option) made the default mailer unconstructible. .env itself is left
alone — that is the operator's live file.

.env.example

@@ -82,7 +82,7 @@ MAIL_FROM_NAME=CluPilot
 # MAIL_PORT=587
 # MAIL_USERNAME=
 # MAIL_PASSWORD=
-# MAIL_SCHEME=tls           # tls | smtps (465)
+# MAIL_SCHEME=smtp          # smtp | smtps (465)
 
 # ═════════════════════════════════════════════════════════════════════════
 #  CluPilot operations — fill these in to run real provisioning.