feat(crypto-tail): 策略最小价差(无/固定/自动) + 前端默认与文案

- 后端: 最小价差 DB/Entity/DTO、Binance K线 REST+WS、自动价差 IQR 预计算与执行时校验
- 前端: 最小价差(自动-固定-无)，默认自动，label 旁 info 说明，选择自动不展示建议约
- i18n: minSpreadModeTip 说明不写死标的
- 文档: crypto-tail-strategy-min-spread-flow.md
- scripts: Binance K线拉取与 WS 示例

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

frontend/src/locales/en/common.json

@@ -1445,7 +1445,14 @@
       "create": "Create",
       "update": "Update",
       "timeWindowStartLEEnd": "Window start must not be greater than end",
-      "timeWindowExceed": "Time window must not exceed period length"
+      "timeWindowExceed": "Time window must not exceed period length",
+      "minSpreadMode": "Min spread",
+      "minSpreadModeTip": "Whether to place an order is based on the spread between open and close in the current period. Auto: system computes a suggested spread from the last 30 klines (updated each period); Fixed: you enter a value (e.g. 30), order only when spread ≥ that value; None: no spread check, order when price is in range.",
+      "minSpreadModeNone": "None",
+      "minSpreadModeFixed": "Fixed",
+      "minSpreadModeAuto": "Auto",
+      "minSpreadValue": "Min spread value (USDC)",
+      "minSpreadValuePlaceholder": "e.g. 30"
     },
     "redeemRequiredModal": {
       "title": "Configure Auto Redeem First",

frontend/src/locales/zh-CN/common.json

@@ -1444,7 +1444,14 @@
       "create": "创建",
       "update": "更新",
       "timeWindowStartLEEnd": "时间区间开始不能大于结束",
-      "timeWindowExceed": "时间区间不能超过周期长度"
+      "timeWindowExceed": "时间区间不能超过周期长度",
+      "minSpreadMode": "最小价差",
+      "minSpreadModeTip": "根据当前周期开盘价与收盘价的价差决定是否下单。自动：系统按历史 30 根 K 线计算建议价差（每周期更新）；固定：您输入一个数值（如 30），仅当价差 ≥ 该值时才下单；无：不校验价差，满足价格区间即下单。",
+      "minSpreadModeNone": "无",
+      "minSpreadModeFixed": "固定",
+      "minSpreadModeAuto": "自动",
+      "minSpreadValue": "最小价差数值 (USDC)",
+      "minSpreadValuePlaceholder": "如 30"
     },
     "redeemRequiredModal": {
       "title": "请先配置自动赎回",

frontend/src/locales/zh-TW/common.json

@@ -1445,7 +1445,14 @@
       "create": "創建",
       "update": "更新",
       "timeWindowStartLEEnd": "時間區間開始不能大於結束",
-      "timeWindowExceed": "時間區間不能超過週期長度"
+      "timeWindowExceed": "時間區間不能超過週期長度",
+      "minSpreadMode": "最小價差",
+      "minSpreadModeTip": "依當前週期開盤價與收盤價的價差決定是否下單。自動：系統依歷史 30 根 K 線計算建議價差（每週期更新）；固定：您輸入一個數值（如 30），僅當價差 ≥ 該值時才下單；無：不校驗價差，滿足價格區間即下單。",
+      "minSpreadModeNone": "無",
+      "minSpreadModeFixed": "固定",
+      "minSpreadModeAuto": "自動",
+      "minSpreadValue": "最小價差數值 (USDC)",
+      "minSpreadValuePlaceholder": "如 30"
     },
     "redeemRequiredModal": {
       "title": "請先配置自動贖回",