fix: Add phantom trade detection and prevention safeguards

**Root Causes:**
1. Auto-flip logic could create phantom trades if close failed
2. Position size mismatches (0.01 SOL vs 11.92 SOL expected) not caught
3. Multiple trades for same symbol+direction in database

**Preventive Measures:**

1. **Startup Validation (lib/startup/init-position-manager.ts)**
   - Validates all open trades against Drift positions on startup
   - Auto-closes phantom trades with <50% expected size
   - Logs size mismatches for manual review
   - Prevents Position Manager from tracking ghost positions

2. **Duplicate Position Prevention (app/api/trading/execute/route.ts)**
   - Blocks opening same-direction position on same symbol
   - Returns 400 error if duplicate detected
   - Only allows auto-flip (opposite direction close + open)

3. **Runtime Phantom Detection (lib/trading/position-manager.ts)**
   - Checks position size every 2s monitoring cycle
   - Auto-closes if size ratio <50% (extreme mismatch)
   - Logs as 'manual' exit with AUTO_CLEANUP tx
   - Removes from monitoring immediately

4. **Quality Score Fix (app/api/trading/check-risk/route.ts)**
   - Hardcoded minScore=60 (removed non-existent config reference)

**Prevention Summary:**
- ✅ Startup validation catches historical phantoms
- ✅ Duplicate check prevents new phantoms
- ✅ Runtime detection catches size mismatches <30s after they occur
- ✅ All three layers work together for defense-in-depth

Issue: User had LONG (phantom) + SHORT (undersized 0.01 SOL vs 11.92 expected)
Fix: Both detected and closed, bot now clean with 0 active trades

app/api/trading/execute/route.ts

@@ -213,6 +213,23 @@ export async function POST(request: NextRequest): Promise<NextResponse<ExecuteTr
       trade => trade.symbol === driftSymbol && trade.direction !== body.direction
     )
     
+    // SAFETY CHECK: Prevent multiple positions on same symbol
+    const sameDirectionPosition = existingTrades.find(
+      trade => trade.symbol === driftSymbol && trade.direction === body.direction
+    )
+    
+    if (sameDirectionPosition) {
+      console.log(`⛔ DUPLICATE POSITION BLOCKED: Already have ${body.direction} position on ${driftSymbol}`)
+      return NextResponse.json(
+        {
+          success: false,
+          error: 'Duplicate position detected',
+          message: `Already have an active ${body.direction} position on ${driftSymbol}. Close it first.`,
+        },
+        { status: 400 }
+      )
+    }
+    
     if (oppositePosition) {
       console.log(`🔄 Signal flip detected! Closing ${oppositePosition.direction} to open ${body.direction}`)