docs: fix multi-channel template example missing required from fields

[Copilot]

The multi-channel messaging example omitted from on both EMAIL and TWILIO entries, making the snippet invalid against EmailTemplateType and SMSTemplateType (both require from: string).

Changes

• docs/docs/platform-configuration/messaging.md: Added from to the EMAIL and TWILIO inputs in the multi-channel example; added inline comment on TWILIO noting from can be omitted when TWILIO_SMS_FROM env var is set (the adapter's actual fallback behavior)

return [
  {
    type: 'EMAIL',
    input: {
      from: 'shop@example.com',  // required
      to: 'admin@example.com',
      subject: `New order #${order.orderNumber}`,
      text: `Order total: ${order.pricing?.total}`,
    },
  },
  {
    type: 'TWILIO',
    input: {
      from: '+15550001234', // Omit if TWILIO_SMS_FROM env var is set
      to: '+41791234567',
      text: `New order #${order.orderNumber}`,
    },
  },
];

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