feat: switch from Helius to Alchemy RPC provider

Changes:
- Updated SOLANA_RPC_URL to use Alchemy (https://solana-mainnet.g.alchemy.com/v2/...)
- Migrated from Helius free tier to Alchemy free tier
- Includes previous rate limit fixes (8s backoff, 2s operation delays)

Context:
- Helius free tier: 10 req/sec sustained, 100 req/sec burst
- Alchemy free tier: 300M compute units/month (more generous)
- User hit 239 rate limit errors in 10 minutes on Helius
- User registered Alchemy account and provided API key

Impact:
- Should significantly reduce 429 rate limit errors
- Better free tier limits for trading bot operations
- Combined with delay fixes for optimal RPC usage

lib/drift/orders.ts

@@ -654,7 +654,7 @@ export async function closePosition(
 async function retryWithBackoff<T>(
   fn: () => Promise<T>,
   maxRetries: number = 3,
-  baseDelay: number = 5000 // Increased from 2s to 5s: 5s → 10s → 20s progression
+  baseDelay: number = 8000 // Increased from 5s to 8s: 8s → 16s → 32s progression for better RPC recovery
 ): Promise<T> {
   const startTime = Date.now()