fix: remove colon from SMTP_TLS value

Environment variables are strings. Use 'never' not ':never' so
the Elixir code can convert it to an atom properly.

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude <noreply@anthropic.com>

asciinema/compose.yaml

@@ -18,7 +18,7 @@ services:
       SMTP_PORT: ${EMAIL_SMTP_PORT}
       SMTP_USERNAME: ${EMAIL_SMTP_USER}
       SMTP_PASSWORD: ${EMAIL_SMTP_PASSWORD}
-      SMTP_TLS: :never
+      SMTP_TLS: never
       SMTP_SSL: true
       SMTP_AUTH: always
       MAIL_FROM_ADDRESS: ${EMAIL_FROM}