优化跟单过滤逻辑和卖出价格计算

- 优化订单簿请求：仅在需要时请求，避免不必要的API调用
- 卖出价格改为市价卖出：优先使用订单簿bestBid，失败则使用Leader价格，固定按90%计算
- 价格容忍度默认值：如果为0，自动使用5%
- 使用枚举和数据类优化checkFilters方法：
  - 新增FilterResult数据类和FilterStatus枚举
  - 移除无用字段isBuyOrder参数
  - 使用类型安全的枚举替代字符串判断
- 优化代码结构：减少if-else嵌套，使用链式调用
- 移除最小订单簿深度功能（minOrderbookDepth）
- 优化最小订单深度逻辑：检查所有方向（买盘+卖盘）的总深度

frontend/src/locales/en/common.json

@@ -597,10 +597,10 @@
     "priceToleranceTooltip": "Allowed adjustment range for copy price based on Leader price, used to adjust price within Leader price ± tolerance range to improve fill rate. For example: set to 5%, Leader price is 0.5, then copy price can be in 0.475-0.525 range.",
     "priceTolerancePlaceholder": "Default 5% (optional)",
     "minOrderDepth": "Min Order Depth (USDC)",
-    "minOrderDepthTooltip": "Minimum order depth (USDC amount), NULL means this filter is not enabled. Ensures market has sufficient liquidity",
+    "minOrderDepthTooltip": "Check total order amount (bids + asks) in orderbook to ensure sufficient liquidity. Leave empty to disable",
     "minOrderDepthPlaceholder": "For example: 100 (optional, leave empty to disable)",
     "maxSpread": "Max Spread (Absolute Price)",
-    "maxSpreadTooltip": "Maximum spread (absolute price), NULL means this filter is not enabled. Avoid copying in markets with excessive spreads",
+    "maxSpreadTooltip": "Maximum spread (absolute price). Avoid copying in markets with excessive spreads. Leave empty to disable",
     "maxSpreadPlaceholder": "For example: 0.05 (5 cents, optional, leave empty to disable)",
     "minOrderbookDepth": "Min Orderbook Depth (USDC)",
     "minOrderbookDepthTooltip": "Minimum orderbook depth (USDC amount), NULL means this filter is not enabled. Check depth of first N levels",
@@ -654,10 +654,10 @@
     "priceToleranceTooltip": "Allowed adjustment range for copy price based on Leader price, used to adjust price within Leader price ± tolerance range to improve fill rate. For example: set to 5%, Leader price is 0.5, then copy price can be in 0.475-0.525 range.",
     "priceTolerancePlaceholder": "Default 5% (optional)",
     "minOrderDepth": "Min Order Depth (USDC)",
-    "minOrderDepthTooltip": "Minimum order depth (USDC amount), NULL means this filter is not enabled. Ensures market has sufficient liquidity",
+    "minOrderDepthTooltip": "Check total order amount (bids + asks) in orderbook to ensure sufficient liquidity. Leave empty to disable",
     "minOrderDepthPlaceholder": "For example: 100 (optional, leave empty to disable)",
     "maxSpread": "Max Spread (Absolute Price)",
-    "maxSpreadTooltip": "Maximum spread (absolute price), NULL means this filter is not enabled. Avoid copying in markets with excessive spreads",
+    "maxSpreadTooltip": "Maximum spread (absolute price). Avoid copying in markets with excessive spreads. Leave empty to disable",
     "maxSpreadPlaceholder": "For example: 0.05 (5 cents, optional, leave empty to disable)",
     "minOrderbookDepth": "Min Orderbook Depth (USDC)",
     "minOrderbookDepthTooltip": "Minimum orderbook depth (USDC amount), NULL means this filter is not enabled. Check depth of first N levels",
@@ -719,10 +719,10 @@
     "delaySecondsPlaceholder": "Default 0 (copy immediately)",
     "filterConditions": "Filter Conditions (Optional)",
     "minOrderDepth": "Min Order Depth (USDC)",
-    "minOrderDepthTooltip": "Minimum order depth (USDC amount), NULL means this filter is not enabled. Ensures market has sufficient liquidity",
+    "minOrderDepthTooltip": "Check total order amount (bids + asks) in orderbook to ensure sufficient liquidity. Leave empty to disable",
     "minOrderDepthPlaceholder": "For example: 100 (optional, leave empty to disable)",
     "maxSpread": "Max Spread (Absolute Price)",
-    "maxSpreadTooltip": "Maximum spread (absolute price), NULL means this filter is not enabled. Avoid copying in markets with excessive spreads",
+    "maxSpreadTooltip": "Maximum spread (absolute price). Avoid copying in markets with excessive spreads. Leave empty to disable",
     "maxSpreadPlaceholder": "For example: 0.05 (5 cents, optional, leave empty to disable)",
     "minOrderbookDepth": "Min Orderbook Depth (USDC)",
     "minOrderbookDepthTooltip": "Minimum orderbook depth (USDC amount), NULL means this filter is not enabled. Check depth of first N levels",
@@ -794,10 +794,10 @@
     "delaySecondsPlaceholder": "Default 0 (copy immediately)",
     "filterConditions": "Filter Conditions (Optional)",
     "minOrderDepth": "Min Order Depth (USDC)",
-    "minOrderDepthTooltip": "Minimum order depth (USDC amount), NULL means this filter is not enabled",
+    "minOrderDepthTooltip": "Check total order amount (bids + asks) in orderbook to ensure sufficient liquidity. Leave empty to disable",
     "minOrderDepthPlaceholder": "For example: 100 (optional, leave empty to disable)",
     "maxSpread": "Max Spread (Absolute Price)",
-    "maxSpreadTooltip": "Maximum spread (absolute price), NULL means this filter is not enabled",
+    "maxSpreadTooltip": "Maximum spread (absolute price). Avoid copying in markets with excessive spreads. Leave empty to disable",
     "maxSpreadPlaceholder": "For example: 0.05 (5 cents, optional, leave empty to disable)",
     "minOrderbookDepth": "Min Orderbook Depth (USDC)",
     "minOrderbookDepthTooltip": "Minimum orderbook depth (USDC amount), NULL means this filter is not enabled",