feat: Add Hyperliquid exchange support with unified trader interface

Major changes:
- Add full Hyperliquid trading support (long/short, leverage, SL/TP)
- Create unified Trader interface for multi-exchange support
- Implement automatic precision handling for orders and prices
- Fix balance calculation and unrealized P&L display
- Add comprehensive configuration guide in README

New features:
- Support for both Binance and Hyperliquid exchanges
- Automatic order size precision based on szDecimals
- Price formatting with 5 significant figures
- Non-custodial trading with Ethereum private key
- Seamless exchange switching via configuration

Technical details:
- Add trader/interface.go for unified trader interface
- Add trader/hyperliquid_trader.go for Hyperliquid implementation
- Update manager and auto_trader to support multiple exchanges
- Add go-hyperliquid SDK dependency
- Fix precision errors (float_to_wire, invalid price)

Fixes:
- Correct calculation of wallet balance and unrealized P&L
- Proper handling of AccountValue vs TotalRawUsd
- Frontend display issues for total equity and P&L

Documentation:
- Add Hyperliquid setup guide in README
- Update config.json.example with both exchanges
- Add troubleshooting section for common errors

Tested with live trading on Hyperliquid mainnet.
No breaking changes - backward compatible with existing configs.

trader/interface.go

@@ -0,0 +1,41 @@
+package trader
+
+// Trader 交易器统一接口
+// 支持多个交易平台（币安、Hyperliquid等）
+type Trader interface {
+	// GetBalance 获取账户余额
+	GetBalance() (map[string]interface{}, error)
+
+	// GetPositions 获取所有持仓
+	GetPositions() ([]map[string]interface{}, error)
+
+	// OpenLong 开多仓
+	OpenLong(symbol string, quantity float64, leverage int) (map[string]interface{}, error)
+
+	// OpenShort 开空仓
+	OpenShort(symbol string, quantity float64, leverage int) (map[string]interface{}, error)
+
+	// CloseLong 平多仓（quantity=0表示全部平仓）
+	CloseLong(symbol string, quantity float64) (map[string]interface{}, error)
+
+	// CloseShort 平空仓（quantity=0表示全部平仓）
+	CloseShort(symbol string, quantity float64) (map[string]interface{}, error)
+
+	// SetLeverage 设置杠杆
+	SetLeverage(symbol string, leverage int) error
+
+	// GetMarketPrice 获取市场价格
+	GetMarketPrice(symbol string) (float64, error)
+
+	// SetStopLoss 设置止损单
+	SetStopLoss(symbol string, positionSide string, quantity, stopPrice float64) error
+
+	// SetTakeProfit 设置止盈单
+	SetTakeProfit(symbol string, positionSide string, quantity, takeProfitPrice float64) error
+
+	// CancelAllOrders 取消该币种的所有挂单
+	CancelAllOrders(symbol string) error
+
+	// FormatQuantity 格式化数量到正确的精度
+	FormatQuantity(symbol string, quantity float64) (string, error)
+}