feat: 所有参数移至config.json, 重构退出逻辑, 清理遗留接口

- 将所有硬编码参数迁移到 config.json (手续费率、止盈/止损阈值、
  超时、腿间隔、加仓步进等)
- 退出条件: 净利 >= take_profit_pct 止盈, 价差 <= 0 平仓
- 删除 Binance/dYdX 遗留代码
- 更新 README 文档
- Dashboard: 双交易所价格表、黑名单UI、按币名排序持仓
- Bitget WS: 文本ping保活
- 数据库: 重置, 无历史仓位

config.json

@@ -3,9 +3,21 @@
   "trade_enabled": true,
   "arb_threshold": 0.03,
   "scan_interval_ms": 200,
-  "trade_threshold": 0.05,
+  "trade_threshold": 0.10,
   "trade_amount_usd": 5,
   "trade_cooldown_ms": 30000,
   "alert_cooldown_sec": 300,
-  "mock_slippage_pct": 0.005
+  "mock_slippage_pct": 0.005,
+  "max_positions": 5,
+  "blacklist_duration_sec": 3600,
+  "initial_capital": 1000,
+  "taker_fee_bitget": 0.060,
+  "taker_fee_hyperliquid": 0.045,
+  "take_profit_pct": 0.20,
+  "spread_reverse_exit_pct": 0,
+  "position_timeout_sec": 1800,
+  "leg_delay_ms": 300,
+  "reversal_tolerance_pct": 0.1,
+  "scale_step_pct": 0.10,
+  "scale_cooldown_sec": 5
 }