feat(frontend): 手动下单功能增强与金额模式支持

- 后端返回 amountMode 和 amountValue 字段，支持前端获取策略配置
- 手动下单确认弹窗显示用户可用余额（绿色高亮）
- 价格输入框右侧添加"获取最新价"按钮，支持实时更新价格
- 数量输入框右侧添加"最大"按钮，根据余额自动计算最大购买数量
- 修正数量计算逻辑：FIXED 和 RATIO 模式均按实际金额计算数量，保留2位小数
  - FIXED 模式：使用配置的固定金额
  - RATIO 模式：按比例计算可用余额
- 数量计算使用保留小数方式（而非向上取整），确保精确匹配投入金额
  - 示例：固定1U，价格0.4，自动填充2.5张
  - 示例：比例30%，余额20U，价格0.4，自动填充15张

Made-with: Cursor

frontend/src/locales/en/common.json

@@ -1676,7 +1676,16 @@
       "failed": "Manual order failed: {{reason}}",
       "errorSigning": "Signing failed: {reason}",
       "errorNetwork": "Network error, please try again later",
-      "priceNotLoaded": "Price data not loaded"
+      "priceNotLoaded": "Price data not loaded",
+      "insufficientBalance": "Insufficient balance, available amount less than 1 USDC",
+      "fetchBalanceFailed": "Failed to fetch account balance",
+      "availableBalance": "Available Balance",
+      "fetchLatestPrice": "Latest Price",
+      "priceUpdated": "Price updated",
+      "maxSize": "Max",
+      "invalidPriceOrBalance": "Invalid price or balance",
+      "insufficientBalanceForMax": "Insufficient balance for max size",
+      "maxSizeUpdated": "Updated to max size"
     }
   }
 }