fix: KuCoin timestamp sync, improve no-coins handling, update README icons

- Add server time synchronization for KuCoin API to fix timestamp error (400002)
- Return empty list instead of error when no available coins (ai500.go)
- Save cycle record even when no candidate coins (show in frontend without red error)
- Update Claude icon to Anthropic dark brand color (#141413)
- Add exchange and AI model icons to README.md and README.ja.md

trader/auto_trader.go

@@ -578,9 +578,19 @@ func (at *AutoTrader) runCycle() error {
 	// NOTE: Must be called BEFORE candidate coins check to ensure equity is always recorded
 	at.saveEquitySnapshot(ctx)
 
-	// 如果没有候选币种，友好提示并跳过本周期
+	// 如果没有候选币种，记录但不报错
 	if len(ctx.CandidateCoins) == 0 {
 		logger.Infof("ℹ️  No candidate coins available, skipping this cycle")
+		record.Success = true // 不是错误，只是没有候选币
+		record.ExecutionLog = append(record.ExecutionLog, "No candidate coins available, cycle skipped")
+		record.AccountState = store.AccountSnapshot{
+			TotalBalance:          ctx.Account.TotalEquity,
+			AvailableBalance:      ctx.Account.AvailableBalance,
+			TotalUnrealizedProfit: ctx.Account.UnrealizedPnL,
+			PositionCount:         ctx.Account.PositionCount,
+			InitialBalance:        at.initialBalance,
+		}
+		at.saveDecision(record)
 		return nil
 	}