feat(frontend): 优化导入账户弹窗与文案

- 导入弹窗：增加步骤条、导入方式改为按钮、代理选项卡片紧凑展示
- 代理选项：标题改为「请选择账户类型」，地址完整显示，有资产标绿，小白说明放入卡片内
- 私钥/助记词：输入框默认两行、禁止换行（换行自动转空格/去除）
- 多语言：新增 proxyAddressHelp，更新 selectProxyOption 文案
- Modal 宽度与内边距微调；PositionList 移除未使用 useRef

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

frontend/src/locales/en/common.json

@@ -214,7 +214,7 @@
     "walletType": "Wallet Type",
     "walletTypeHelp": "Web3 Wallet: Polymarket accounts connected via browser wallets like MetaMask\nMagic: Polymarket accounts logged in via email or social accounts (Google, Twitter, etc.)",
     "loadingProxyOptions": "Loading proxy addresses and asset information...",
-    "selectProxyOption": "Please select a proxy address",
+    "selectProxyOption": "Please select account type",
     "proxyOptionRequired": "Please select a proxy address",
     "proxyOption": {
       "magic": {
@@ -226,6 +226,7 @@
         "title": "Safe Proxy Address"
       },
       "proxyAddress": "Proxy Address",
+      "proxyAddressHelp": "The proxy address is the wallet address you actually use on Polymarket: Magic for email/social login accounts, Safe for browser wallet (e.g. MetaMask) accounts. Please select the one that matches how you log in to Polymarket.",
       "availableBalance": "Available Balance",
       "positionBalance": "Position Balance",
       "totalBalance": "Total Balance",

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

@@ -213,7 +213,7 @@
     "walletType": "钱包类型",
     "walletTypeHelp": "Web3钱包：使用 MetaMask 等浏览器钱包连接的 Polymarket 账户\nMagic：通过邮箱或社交账号（如 Google、Twitter）登录的 Polymarket 账户",
     "loadingProxyOptions": "正在获取代理地址和资产信息...",
-    "selectProxyOption": "请选择代理地址",
+    "selectProxyOption": "请选择账户类型",
     "proxyOptionRequired": "请选择一个代理地址",
     "proxyOption": {
       "magic": {
@@ -225,6 +225,7 @@
         "title": "Safe 代理地址"
       },
       "proxyAddress": "代理地址",
+      "proxyAddressHelp": "代理地址是您在 Polymarket 上实际使用的钱包地址：Magic 为邮箱/社交登录账户，Safe 为浏览器钱包（如 MetaMask）账户。请选择与您 Polymarket 登录方式一致的一项。",
       "availableBalance": "可用余额",
       "positionBalance": "仓位余额",
       "totalBalance": "总余额",

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

@@ -214,7 +214,7 @@
     "walletType": "錢包類型",
     "walletTypeHelp": "Web3錢包：使用 MetaMask 等瀏覽器錢包連接的 Polymarket 帳戶\nMagic：透過郵箱或社群帳號（如 Google、Twitter）登入的 Polymarket 帳戶",
     "loadingProxyOptions": "正在獲取代理地址和資產信息...",
-    "selectProxyOption": "請選擇代理地址",
+    "selectProxyOption": "請選擇帳戶類型",
     "proxyOptionRequired": "請選擇一個代理地址",
     "proxyOption": {
       "magic": {
@@ -226,6 +226,7 @@
         "title": "Safe 代理地址"
       },
       "proxyAddress": "代理地址",
+      "proxyAddressHelp": "代理地址是您在 Polymarket 上實際使用的錢包地址：Magic 為郵箱/社群登入帳戶，Safe 為瀏覽器錢包（如 MetaMask）帳戶。請選擇與您 Polymarket 登入方式一致的一項。",
       "availableBalance": "可用餘額",
       "positionBalance": "倉位餘額",
       "totalBalance": "總餘額",