CRITICAL FIX: Use ?? instead of || for tp2SizePercent to allow 0 value

BUG FOUND:
Line 558: tp2SizePercent: config.takeProfit2SizePercent || 100

When config.takeProfit2SizePercent = 0 (TP2-as-runner system), JavaScript's ||
operator treats 0 as falsy and falls back to 100, causing TP2 to close 100%
of remaining position instead of activating trailing stop.

IMPACT:
- On-chain orders placed correctly (line 481 uses ?? correctly)
- Position Manager reads from DB and expects TP2 to close position
- Result: User sees TWO take-profit orders instead of runner system

FIX:
Changed both tp1SizePercent and tp2SizePercent to use ?? operator:
- tp1SizePercent: config.takeProfit1SizePercent ?? 75
- tp2SizePercent: config.takeProfit2SizePercent ?? 0

This allows 0 value to be saved correctly for TP2-as-runner system.

VERIFICATION NEEDED:
Current open SHORT position in database has tp2SizePercent=100 from before
this fix. Next trade will use correct runner system.

app/api/trading/sync-positions/route.ts

@@ -22,7 +22,7 @@ export async function POST(request: NextRequest): Promise<NextResponse> {
     console.log('🔄 Position sync requested...')
 
     const config = getMergedConfig()
-    const driftService = await getDriftService()
+    const driftService = await initializeDriftService()
     const positionManager = await getInitializedPositionManager()
     const prisma = getPrismaClient()