feat: Add trader enabled switch and fix critical bugs

New Features:
- Add 'enabled' field to trader config for selective startup
- Only enabled traders will be initialized and run
- Display skip messages for disabled traders in logs

Bug Fixes:
- Fix Hyperliquid account value calculation
  * AccountValue is total equity, no need to add TotalMarginUsed
  * Correctly calculate wallet balance without unrealized PnL
  * Fix available balance calculation (AccountValue - TotalMarginUsed)
- Fix frontend page refresh navigation issue
  * Use URL hash to persist page state across refreshes
  * Support browser back/forward buttons
  * Prevent Details page from reverting to Competition on refresh

Technical Changes:
- config/config.go: Add Enabled bool field to TraderConfig
- main.go: Skip disabled traders during initialization
- trader/hyperliquid_trader.go: Correct account value logic
- web/src/App.tsx: Implement hash-based routing

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude <noreply@anthropic.com>

config/config.go

@@ -11,6 +11,7 @@ import (
 type TraderConfig struct {
 	ID      string `json:"id"`
 	Name    string `json:"name"`
+	Enabled bool   `json:"enabled"` // 是否启用该trader
 	AIModel string `json:"ai_model"` // "qwen" or "deepseek"
 
 	// 交易平台选择（二选一）