feat: Add distinction between regular SL and trailing SL

User Request: Distinguish between SL and Trailing SL in analytics overview

Changes:
1. Position Manager:
   - Updated ExitResult interface to include 'TRAILING_SL' exit reason
   - Modified trailing stop exit (line 1457) to use 'TRAILING_SL' instead of 'SL'
   - Enhanced external closure detection (line 937) to identify trailing stops
   - Updated handleManualClosure to detect trailing SL at price target

2. Database:
   - Updated UpdateTradeExitParams interface to accept 'TRAILING_SL'

3. Frontend Analytics:
   - Updated last trade display to show 'Trailing SL' with special formatting
   - Purple background/border for TRAILING_SL vs blue for regular SL
   - Runner emoji (🏃) prefix for trailing stops

Impact:
- Users can now see when trades exit via trailing stop vs regular SL
- Better understanding of runner system performance
- Trailing stops visually distinct in analytics dashboard

Files Modified:
- lib/trading/position-manager.ts (4 locations)
- lib/database/trades.ts (UpdateTradeExitParams interface)
- app/analytics/page.tsx (exit reason display)
- .github/copilot-instructions.md (Common Pitfalls #61, #62)

lib/database/trades.ts

@@ -82,7 +82,7 @@ export interface UpdateTradeStateParams {
 export interface UpdateTradeExitParams {
   positionId: string
   exitPrice: number
-  exitReason: 'TP1' | 'TP2' | 'SL' | 'SOFT_SL' | 'HARD_SL' | 'manual' | 'emergency'
+  exitReason: 'TP1' | 'TP2' | 'SL' | 'SOFT_SL' | 'HARD_SL' | 'TRAILING_SL' | 'manual' | 'emergency'
   realizedPnL: number
   exitOrderTx: string
   holdTimeSeconds: number