feat(api): add server IP display for exchange whitelist configuration (#520)

Added functionality to display server public IP address for users to configure exchange API whitelists, specifically for Binance integration.

Backend changes (api/server.go):
- Add GET /api/server-ip endpoint requiring authentication
- Implement getPublicIPFromAPI() with fallback to multiple IP services
- Implement getPublicIPFromInterface() for local network interface detection
- Add isPrivateIP() helper to filter private IP addresses
- Import net package for IP address handling

Frontend changes (web/):
- Add getServerIP() API method in api.ts
- Display server IP in ExchangeConfigModal for Binance
- Add IP copy-to-clipboard functionality
- Load and display server IP when Binance exchange is selected
- Add i18n translations (en/zh) for whitelist IP messages:
  - whitelistIP, whitelistIPDesc, serverIPAddresses
  - copyIP, ipCopied, loadingServerIP

User benefits:
- Simplifies Binance API whitelist configuration
- Shows exact server IP to add to exchange whitelist
- One-click IP copy for convenience

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-authored-by: Claude <noreply@anthropic.com>

web/src/i18n/translations.ts

@@ -291,6 +291,12 @@ export const translations = {
     viewGuide: 'View Guide',
     binanceSetupGuide: 'Binance Setup Guide',
     closeGuide: 'Close',
+    whitelistIP: 'Whitelist IP',
+    whitelistIPDesc: 'Binance requires adding server IP to API whitelist',
+    serverIPAddresses: 'Server IP Addresses',
+    copyIP: 'Copy',
+    ipCopied: 'IP Copied',
+    loadingServerIP: 'Loading server IP...',
 
     // Error Messages
     createTraderFailed: 'Failed to create trader',
@@ -758,6 +764,12 @@ export const translations = {
     viewGuide: '查看教程',
     binanceSetupGuide: '币安配置教程',
     closeGuide: '关闭',
+    whitelistIP: '白名单IP',
+    whitelistIPDesc: '币安交易所需要填写白名单IP',
+    serverIPAddresses: '服务器IP地址',
+    copyIP: '复制',
+    ipCopied: 'IP已复制',
+    loadingServerIP: '正在加载服务器IP...',
 
     // Error Messages
     createTraderFailed: '创建交易员失败',