feat: integrate promoseven/azure-mailer as mail transport

Adds path repository, composer dependency, azure mailer config entry,
and AZURE_* env vars to .env.example.

Co-Authored-By: Claude Sonnet 4.6 <[email protected]>

.env.example

@@ -69,3 +69,9 @@ ULTRAMSG_TOKEN=
 ULTRAMSG_WEBHOOK_SECRET=
 ULTRAMSG_WEBHOOK_PATH=ultra-message/webhook
 ULTRAMSG_ENABLED=true
+
+# Microsoft 365 / Azure AD Mail
+AZURE_TENANT_ID=
+AZURE_CLIENT_ID=
+AZURE_CLIENT_SECRET=
+AZURE_MAIL_FROM_ADDRESS=