feat: enforce communication channel from routing config

Context

The multi-contact system includes a communication_routing table with a channel field (EMAIL, SMS, EMAIL_AND_SMS) per communication type. Currently this field is saved but not enforced — the decision to send email vs SMS is hardcoded in each service.

Current behavior

• resolveContact(customerId, communicationType) returns the contact (email/phone) but not the channel
• Each sender independently decides whether to send email, SMS, or both
• The channel column in communication_routing is purely documentative

Desired behavior

• resolveContact should also return the configured channel
• Each sender should respect the channel setting:
• EMAIL → only send email, skip SMS
• SMS → only send SMS, skip email
• EMAIL_AND_SMS → send both (current default behavior)
• The routing UI (/settings/communication-routing) already allows changing the channel — it just needs to be wired up

Affected services

All services that call resolveContact and send communications:

• contract-signing.service.ts (CONTRACT_INVITE, CONTRACT_OTP, CONTRACT_SIGNED_COPY)
• contract-reminders.ts (CONTRACT_REMINDER)
• delivery.service.ts (DELIVERY_CONFIRMATION)
• availability.service.ts (AVAILABILITY_REQUEST/CONFIRMATION/CANCELLATION)
• collection-manager.ts (COLLECTION_REMINDER_AUTO)
• collections.ts (COLLECTION_REMINDER_MANUAL)
• invoices.ts (INVOICE_EMAIL)
• invoice-courtesy.service.ts (INVOICE_COURTESY_COPY)
• ddts.ts (DDT_CONFIRMATION)
• auto-pay.service.ts (AUTOPAY_*)
• draft-notifier.ts, printing-orders.ts, portal.ts

Implementation plan

1. Extend resolveContact return type to include channel: string
2. Update ResolvedContact interface
3. Each sender checks contact.channel before deciding email/SMS
4. Add helper: shouldSendEmail(channel), shouldSendSms(channel)

Priority

Low — the system works correctly now, this is an optimization for configurability.