fix: prevent panics from unsafe type assertions in trading code + add request body limit

Security & Reliability:
- Add requestBodyLimitMiddleware (1MB) to prevent OOM from oversized API payloads
- Fix defer resp.Body.Close() inside loop in getPublicIPFromAPI (connection leak)
- Add posFloat64/posString safe helpers for position map access

Panic Prevention (critical for trading):
- Convert 30+ unsafe type assertions (pos["key"].(type)) to safe comma-ok
  pattern across all exchange traders: OKX, Hyperliquid, Aster, Bybit,
  KuCoin, Gate, Bitget, Binance
- Fix auto_trader_risk.go: drawdown monitor could panic and silently stop
  monitoring, leaving positions unprotected
- Fix auto_trader_decision.go & auto_trader_loop.go: core trading loop
  position parsing now crash-proof
- All trader/ code now has zero unsafe type assertions

Frontend:
- Fix config.ts: rejected promise cached forever on network error (never retries)

web/src/lib/config.ts

@@ -19,6 +19,11 @@ export function getSystemConfig(): Promise<SystemConfig> {
       cachedConfig = data
       return data
     })
+    .catch((err) => {
+      // Reset so next call retries instead of returning the rejected promise forever
+      configPromise = null
+      throw err
+    })
   return configPromise
 }