Testnetz: Micro-Order-Minimum + SELL-Proportionalität extrahiert; SELL-Leiter (Phase 0.1) vorbereitet

Weiter im Muster extrahieren->testen (verhaltensneutral, clob.md):
- CopyTradingRisk.IsBelowPolymarketMinimum (Shares < 5.5 || USDC < 0.10) –
  BUY-Micro-Order-Filter verdrahtet + Tests.
- SellLogic.SellProportion (signalSize/(remaining+signalSize), Denominator<=0 -> 0)
  + Konstante MinSignificantSellRatio (0.30); SELL-Proportionalitätscheck der
  Engine ruft sie jetzt (Charakterisierung, sichert Phase-2-Umbau ab).
- SellLogic-Eskalationsleiter (Phase 0.1, NOCH NICHT verdrahtet): FirstLimit
  (HF-fest/prozentual), Floor (SellFloorPct), NextPrice (relative Stufe, auf Floor
  geclamped), IsAtFloor. Reine Grundlage fuer das spaetere SELL-Wiring.
- Tests: CopyTradingRisk-Minimum (5 Faelle) + SellLogicTests (Proportion +
  Leiter). Gesamt 154 gruen.

Build/Smoke gruen.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

src/PolyTrader.Modules.CopyTrading/Services/CopyTradingEngine.cs

@@ -383,7 +383,7 @@ namespace PolyTraderSharp.Services
                         // ===== MICRO-ORDER FILTER: Polymarket Minimum Size Enforcement =====
                         // Polymarket lehnt Orders mit < 5 Shares ab ("Size lower than the minimum: 5").
                         // Statt die API zu belasten und Fehler-Logs zu erzeugen, filtern wir hier sofort.
-                        if (exact.shares < 5.5m || exact.usdc < 0.10m)
+                        if (CopyTradingRisk.IsBelowPolymarketMinimum(exact.shares, exact.usdc))
                         {
                             _logger.TradeReasoning($"❌ Trade BUY [{signal.MarketQuestion}] [{shareType}] gestoppt:\n" +
                                                    $"   Konto:      {account.Name}\n" +
@@ -431,8 +431,9 @@ namespace PolyTraderSharp.Services
                     if (masterShares > 0 && signal.Size > 0)
                     {
                         // Calculate what percentage of the master's known position this SELL represents
-                        decimal sellRatio = signal.Size / (masterShares + signal.Size); // +signal.Size because the position was already reduced
-                        if (sellRatio < 0.30m)
+                        // (Proportionalität: SellLogic, unit-getestet)
+                        decimal sellRatio = SellLogic.SellProportion(masterShares, signal.Size);
+                        if (sellRatio < SellLogic.MinSignificantSellRatio)
                         {
                             _logger.TradeReasoning($"📊 Trade SELL [{signal.MarketQuestion}] [{shareType}] ignoriert:\n" +
                                                    $"   Konto:      {account.Name}\n" +