critical: Fix Layer 2 ghost detection causing duplicate Telegram notifications

Bug: Trade #8 (SHORT SOL-PERP) sent 13 duplicate 'POSITION CLOSED' notifications
- P&L compounded: $11.50 → $38.56 → $64.70 → ... → $155.05
- Root cause: Layer 2 ghost detection (failureCount > 20) didn't check closingInProgress flag
- Called handleExternalClosure() every 2 seconds during rate limit storm (6,581 failures)
- Each call sent Telegram notification with compounding P&L

Fix:
- Added closingInProgress check before Layer 2 ghost detection
- Mark trade as closing BEFORE calling handleExternalClosure()
- Prevents duplicate processing during async database updates

Location: lib/trading/position-manager.ts lines 1477-1490
Prevents: Common Pitfall #49 (P&L compounding) in Layer 2 death spiral scenario
Related: Common Pitfall #40 (ghost death spiral), #48 (closingInProgress flag)

Impact: No more duplicate notifications, accurate P&L reporting

lib/trading/position-manager.ts

@@ -1477,7 +1477,7 @@ export class PositionManager {
           
           // LAYER 2: Death spiral detector (Nov 15, 2025)
           // If we've failed 20+ times, check Drift API to see if it's a ghost position
-          if (trade.priceCheckCount > 20) {
+          if (trade.priceCheckCount > 20 && !trade.closingInProgress) {
             try {
               const driftService = getDriftService()
               const marketConfig = getMarketConfig(trade.symbol)
@@ -1487,6 +1487,11 @@ export class PositionManager {
               if (!position || Math.abs(position.size) < 0.01) {
                 console.log(`🔴 LAYER 2: Ghost detected after ${trade.priceCheckCount} failures`)
                 console.log(`   Drift shows position closed/missing - removing from monitoring`)
+                
+                // CRITICAL: Mark as closing to prevent duplicate processing
+                trade.closingInProgress = true
+                trade.closeConfirmedAt = Date.now()
+                
                 await this.handleExternalClosure(trade, 'Layer 2: Ghost detected via Drift API')
                 return
               } else {