Copy performance fees (Phase 4)

Money-manager performance fees na high-water-mark, standard copy-trading model (cTrader Copy, Darwinex, ZuluTrade profit-share): provider charges procent new profit ponad każdy follower's peak equity — nigdy na opening balance, i nigdy twice dla ground już recovered. Opt-in via App:Copy:FeesEnabled (off domyślnie).

Model (high-water-mark)

Per destination (follower account), każdy settlement:

1. First settlement seeds high-water-mark (HWM) na current equity → no charge (follower jest nigdy billed na swoim deposit).
2. New high (equity > HWM): fee = performanceFeePercent × (equity − HWM), wtedy HWM ← equity.
3. At lub below peak: no fee, HWM unchanged — follower musi first recover past old peak, więc nigdy nie są charged twice dla same gains.

Fee arithmetic to domain invariant na CopyDestination.SettleFee(equity) — aggregate owns to; settlement service tylko supplies polled equity i records returned amount. PerformanceFee to value object capped na 50% więc misconfiguration nie może charge away follower's whole gain.

Jak settles

CopyFeeSettlementService (BackgroundService, tylko gdy FeesEnabled)
   │  każdy App:Copy:FeeSettlementInterval
   ├─ load running profiles z fee-configured destination
   ├─ ICopyEquityReader.ReadEquityAsync(ctid)   ← OpenApiCopyEquityReader otwiera session,
   │                                               computes balance + floating P&L (PropFirmEquityCalculator)
   ├─ destination.SettleFee(equity)             ← HWM logic na aggregate
   └─ persist advanced HWM + append CopyFeeAccrual (tylko na new high)

• ICopyEquityReader to Core abstraction; live implementation (OpenApiCopyEquityReader) to jedyny infra piece — więc settlement + HWM logic jest exercised w tests z fake reader, no live broker.
• CopyFeeAccrual to append-only log (HWM-before, equity, fee %, fee amount, settled-at) — fact log dla fee report i billing, nie aggregate.

Konfiguracja & API

App:Copy ustawienie	Domyślnie	Effect
FeesEnabled	false	Run settlement service.
FeeSettlementInterval	1h	How often equity polled i fees settled.

Per-destination: PerformanceFeePercent (0–50) set na destination (add/edit destination request).

• GET /api/copy/profiles/{id}/fees — profile's fee accruals + total charged.

Testy

• Unit (CopyPerformanceFeeTests) — HWM invariant: first settlement seeds + charges nic; new high charges tylko gain above peak; at/below peak charges nic i peak nigdy nie retreats; after drawdown tylko recovery past old peak jest charged; 0% nigdy charges; VO rejects out-of-range percents.
• Integracja (CopyFeeSettlementTests, real Postgres, fake equity reader) — seed→10k (no charge, mark seeded), 12k (charges 400, mark advances), 11k (no charge, mark held); accrual persisted z right owner/amount.

Copy host jest untouched przez fees (settlement to separate DB job), więc copy DST stress suite jest unaffected (23/23).