chore(email): decommission SMTP2GO references — local MTA only

SMTP2GO is no longer used: Listmonk relays through the local Postfix MTA
(172.18.0.1:25 from the Docker network), which DKIM-signs and delivers
direct-to-recipient-MX; transactional mail goes through Carbonio. Verified
zero smtp2go in any live container env + postfix has no external relayhost.

Removed the stale references so a rebuild/new dev can't re-introduce it:
- api/src/config.ts: SMTP_HOST default mail.smtp2go.com -> co.carrierone.com
- scripts/workers/crypto_payment_worker.py: same default fix
- infra/ansible all.yml: listmonk_smtp_* now 172.18.0.1:25, no auth (+comment)
- app.env.j2 / email.ts / crm.md / go-live-todo.md / architecture.svg: docs

api/src/config.ts

@@ -99,7 +99,7 @@ function loadConfig(): Config {
       webhookSecret: optional("STRIPE_WEBHOOK_SECRET", ""),
     },
     smtp: {
-      host: optional("SMTP_HOST", "mail.smtp2go.com"),
+      host: optional("SMTP_HOST", "co.carrierone.com"),
       port: parseInt(optional("SMTP_PORT", "587"), 10),
       user: optional("SMTP_USER", ""),
       pass: optional("SMTP_PASS", ""),

api/src/email.ts

@@ -6,7 +6,7 @@
  *   - Portal access link emails (JWT-signed links)
  *
  * All transactional emails go through Carbonio: co.carrierone.com:587
- * (SMTP2GO is used only by Listmonk for mass-mail campaigns.)
+ * (Listmonk mass-mail relays through the local Postfix MTA, not this path.)
  * Env vars: SMTP_HOST, SMTP_PORT, SMTP_USER, SMTP_PASS, SMTP_FROM
  */