Add Discord bot services for assignment transfer interactions:
1. transferInteractions.ts: Handle button interactions for transfer requests,
approvals, rejections, appeals, completions, and cancellations.
2. transferRequests.ts: Poll for pending assignment transfers and trigger
notification delivery to Discord when status changes to pending/approved/rejected.
3. transferDelivery.ts: Deliver transfer notifications to users via DMs with
embeds showing status, details, and actions (approve/reject/appeal).
4. transferMessaging.ts: Provide Discord embed building for transfer messages
with status badges and action buttons.
5. Update bot index.ts: Add transfer button interaction handler with customId prefix "ptf-xfer:"
6. Update notificationBridge.ts: Exclude transfer notification types from general
notification polling to avoid duplication (Phase 2 feature).
Integration: Services are started via src/bot/services/index.ts and run alongside
existing mission and notification services.
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