feat(hyperliquid): Auto-generate wallet address from private key

Enable automatic wallet address generation from private key for Hyperliquid
exchange, simplifying user onboarding and reducing configuration errors.

Backend Changes (trader/hyperliquid_trader.go):
- Import crypto/ecdsa package for ECDSA public key operations
- Enable wallet address auto-generation when walletAddr is empty
- Use crypto.PubkeyToAddress() to derive address from private key
- Add logging for both auto-generated and manually provided addresses

Frontend Changes (web/src/components/AITradersPage.tsx):
- Remove wallet address required validation (only private key required)
- Update button disabled state to only check private key
- Add "Optional" label to wallet address field
- Add dynamic placeholder with bilingual hint
- Show context-aware helper text based on input state
- Remove HTML required attribute from input field

Translation Updates (web/src/i18n/translations.ts):
- Add 'optional' translation (EN: "Optional", ZH: "可选")
- Add 'hyperliquidWalletAddressAutoGenerate' translation
  EN: "Leave blank to automatically generate wallet address from private key"
  ZH: "留空将自动从私钥生成钱包地址"

Benefits:
✅ Simplified UX - Users only need to provide private key
✅ Error prevention - Auto-generated address always matches private key
✅ Backward compatible - Manual address input still supported
✅ Better UX - Clear visual indicators for optional fields

Technical Details:
- Uses Ethereum standard ECDSA public key to address conversion
- Implementation was already present but commented out (lines 37-43)
- No database schema changes required (hyperliquid_wallet_addr already nullable)
- Fallback behavior: manual input > auto-generation

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

Co-Authored-By: Claude <noreply@anthropic.com>

web/src/components/AITradersPage.tsx

@@ -1201,7 +1201,7 @@ function ExchangeConfigModal({
       if (!apiKey.trim() || !secretKey.trim()) return;
       await onSave(selectedExchangeId, apiKey.trim(), secretKey.trim(), testnet);
     } else if (selectedExchange?.id === 'hyperliquid') {
-      if (!apiKey.trim() || !hyperliquidWalletAddr.trim()) return;
+      if (!apiKey.trim()) return; // 只验证私钥，钱包地址可选（会自动生成）
       await onSave(selectedExchangeId, apiKey.trim(), '', testnet, hyperliquidWalletAddr.trim());
     } else if (selectedExchange?.id === 'aster') {
       if (!asterUser.trim() || !asterSigner.trim() || !asterPrivateKey.trim()) return;
@@ -1360,18 +1360,22 @@ function ExchangeConfigModal({
                   <div>
                     <label className="block text-sm font-semibold mb-2" style={{ color: '#EAECEF' }}>
                       {t('walletAddress', language)}
+                      <span className="text-xs font-normal ml-2" style={{ color: '#848E9C' }}>
+                        ({t('optional', language)})
+                      </span>
                     </label>
                     <input
                       type="text"
                       value={hyperliquidWalletAddr}
                       onChange={(e) => setHyperliquidWalletAddr(e.target.value)}
-                      placeholder={t('enterWalletAddress', language)}
+                      placeholder="0x... (留空将自动从私钥生成 / Leave blank to auto-generate)"
                       className="w-full px-3 py-2 rounded"
                       style={{ background: '#0B0E11', border: '1px solid #2B3139', color: '#EAECEF' }}
-                      required
                     />
                     <div className="text-xs mt-1" style={{ color: '#848E9C' }}>
-                      {t('hyperliquidWalletAddressDesc', language)}
+                      {hyperliquidWalletAddr.trim()
+                        ? t('hyperliquidWalletAddressDesc', language)
+                        : t('hyperliquidWalletAddressAutoGenerate', language)}
                     </div>
                   </div>
                 </>
@@ -1468,10 +1472,10 @@ function ExchangeConfigModal({
             <button
               type="submit"
               disabled={
-                !selectedExchange || 
+                !selectedExchange ||
                 (selectedExchange.id === 'binance' && (!apiKey.trim() || !secretKey.trim())) ||
                 (selectedExchange.id === 'okx' && (!apiKey.trim() || !secretKey.trim() || !passphrase.trim())) ||
-                (selectedExchange.id === 'hyperliquid' && (!apiKey.trim() || !hyperliquidWalletAddr.trim())) ||
+                (selectedExchange.id === 'hyperliquid' && !apiKey.trim()) ||  // 只验证私钥，钱包地址可选
                 (selectedExchange.id === 'aster' && (!asterUser.trim() || !asterSigner.trim() || !asterPrivateKey.trim())) ||
                 (selectedExchange.type === 'cex' && selectedExchange.id !== 'hyperliquid' && selectedExchange.id !== 'aster' && selectedExchange.id !== 'binance' && selectedExchange.id !== 'okx' && (!apiKey.trim() || !secretKey.trim()))
               }