feat(swap-service): add affiliate address tracking alongside referral codes

[NeOMakinG]

Summary

Adds B2B affiliate address tracking to swap-service, running alongside the existing referralCode system. Enables tracking swap volumes and fees by Arbitrum address for B2B integrators.

Epic: ss-aff — B2B Affiliate Tracking System (bead 4)

Changes

Prisma Schema (apps/swap-service/prisma/schema.prisma)

• Added affiliateAddress String? field to Swap model
• Added @@index([affiliateAddress]) for query performance

Migration

• 20260223000000_add_affiliate_address — ALTER TABLE "Swap" ADD COLUMN "affiliateAddress" TEXT + index

Swap Service (apps/swap-service/src/swaps/swaps.service.ts)

• createSwap() now accepts and stores affiliateAddress
• sellAmountUsd calculated and snapshot at creation time using getAssetPriceUsd()
• New calculateAffiliateFees() method — queries by affiliateAddress (parallel to calculateReferralFees by referralCode)
• Prefers stored sellAmountUsd snapshot, falls back to live pricing for older swaps

Swap Controller (apps/swap-service/src/swaps/swaps.controller.ts)

• New GET /swaps/affiliate-fees/:affiliateAddress endpoint
• Mirrors existing /swaps/referral-fees/:referralCode pattern

Shared Types (packages/shared-types/src/index.ts)

• Added affiliateAddress?: string to CreateSwapDto

Design Decisions

• Two systems coexist: referralCode (user-to-user) and affiliateAddress (B2B) — both can be set on the same swap
• Snapshot pricing: sellAmountUsd captured at creation time to ensure consistent fee calculations
• Same response shape: { affiliateAddress, swapCount, totalSwapVolumeUsd, totalFeesCollectedUsd, referrerCommissionUsd }
• No changes to existing system: referralCode flow completely untouched

Testing

• Existing referral system unaffected
• New affiliate-fees endpoint returns expected data structure
• Migration applies cleanly

Related PRs

• Web: shapeshift/web — swap-tracking branch (separate PR with public-api endpoints, widget fix, web app attribution, dashboard)

Out of Scope

• Fee distribution/payouts
• Custom fee rates per affiliate
• Multi-chain affiliate addresses