refactor: 尾盘策略统一更名为加密价差策略

- 前端：菜单父级「加密价差策略」，子项「策略配置」「实时监控」；i18n 与类型注释全部替换
- 后端：i18n、ErrorCode、DTO/实体/服务注释与日志「尾盘」→「加密价差策略」；TG 通知文案
- 文档：README、中英文用户指南、UI 规格、任务、流程、价差流程、市场数据、动态系数等全部更新
- 不修改 API 路径、路由、表名与类名，保持兼容

Co-authored-by: Cursor <cursoragent@cursor.com>

frontend/src/locales/en/common.json

@@ -312,9 +312,9 @@
     "leaders": "Leader Management",
     "templates": "Templates",
     "copyTradingConfig": "Copy Trading Config",
-    "cryptoTail": "Crypto Tail",
-    "cryptoTailStrategy": "Tail Strategy",
-    "cryptoTailMonitor": "Tail Monitor",
+    "cryptoSpreadStrategy": "Crypto Spread Strategy",
+    "cryptoTailStrategy": "Strategy Config",
+    "cryptoTailMonitor": "Real-time Monitor",
     "positions": "Position Management",
     "backtest": "Backtest",
     "statistics": "Statistics",
@@ -1486,12 +1486,12 @@
   "cryptoTailStrategy": {
     "binanceApiAlert": {
       "title": "Cannot connect to Binance API — strategy cannot run for now",
-      "description": "Tail strategy needs Binance market data to work. The connection failed; this may be a network issue or Binance outage. Try again later by clicking the button below.",
+      "description": "Crypto spread strategy needs Binance market data to work. The connection failed; this may be a network issue or Binance outage. Try again later by clicking the button below.",
       "recheck": "Re-check"
     },
     "list": {
-      "title": "Crypto Tail Strategy",
-      "walletTip": "Use a dedicated wallet for tail strategy. Do not use it for manual trading or copy trading to avoid balance/position issues.",
+      "title": "Crypto Spread Strategy",
+      "walletTip": "Use a dedicated wallet for crypto spread strategy. Do not use it for manual trading or copy trading to avoid balance/position issues.",
       "addStrategy": "Add Strategy",
       "strategyName": "Strategy Name",
       "account": "Account",
@@ -1548,7 +1548,7 @@
     },
     "redeemRequiredModal": {
       "title": "Configure Auto Redeem First",
-      "description": "Tail strategy requires auto redeem. Please configure Builder API Key and enable auto redeem in System Settings.",
+      "description": "Crypto spread strategy requires auto redeem. Please configure Builder API Key and enable auto redeem in System Settings.",
       "goToSettings": "Go to Settings",
       "cancel": "Cancel"
     },
@@ -1579,7 +1579,7 @@
     }
   },
   "cryptoTailMonitor": {
-    "title": "Tail Strategy Monitor",
+    "title": "Crypto Spread Strategy Monitor",
     "selectStrategy": "Strategy",
     "selectStrategyPlaceholder": "Select a strategy to monitor",
     "direction": "Direction",