feat(payouts): implement instructor revenue breakdown and payouts system

[dorismaduegbunam]

Description

This PR introduces the core infrastructure for instructors to view their revenue breakdown, manage their payout profiles, review historical payout records, and receive automated email notifications when a payout is processed.

closes #563

Resolves

• Issue: Instructors should see revenue earned.

Changes Made

• Entities & Relationships
  • Added InstructorPayoutProfile to track instructor preferences (e.g. payout schedule, payment method, details).
  • Added InstructorPayout to act as an immutable ledger of transactions (historical payouts).
• Service & Controller (PayoutsModule)
  • Implemented getRevenueBreakdown which aggregates active Course items, completed Payment records, and processed Refund items to compute Gross Revenue, Total Refunds, and Net Revenue globally and per-course.
  • Implemented secure CRUD endpoints for managing settings and fetching historical payouts.
  • Provided an admin-facing process endpoint to record payouts and trigger automated email logic.
• Email Notifications
  • Injected an instructor_payout template configuration into the NotificationTemplateService seed.
  • Integrated payout execution directly with NotificationsService with graceful fallbacks if the templated engine drops.
• Housekeeping
  • Resolved an untracked syntax and duplicate definition bug within notifications.service.ts and notifications.queue.ts caused by an earlier merge conflict upstream.

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