fix: Complete i18n implementation for English language display

This commit addresses the issue where switching to English still showed Chinese text in many UI elements.

Changes made:
- Added 40+ missing translation keys to translations.ts for both English and Chinese
- Updated App.tsx to use t() function for all hardcoded text (logout button, loading message)
- Updated AITradersPage.tsx extensively:
  - Replaced all alert/confirm messages with translation keys
  - Updated status labels (inUse, enabled, configured)
  - Updated all modal components (SignalSource, ModelConfig, ExchangeConfig)
  - Added language prop to all modal components
  - Replaced all Chinese UI text with translation function calls

The implementation now properly supports language switching between English and Chinese throughout the entire application.

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

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

web/src/App.tsx

@@ -179,7 +179,7 @@ function App() {
                style={{ background: 'linear-gradient(135deg, #F0B90B 0%, #FCD535 100%)' }}>
             ⚡
           </div>
-          <p style={{ color: '#EAECEF' }}>加载中...</p>
+          <p style={{ color: '#EAECEF' }}>{t('loading', language)}</p>
         </div>
       </div>
     );
@@ -299,7 +299,7 @@ function App() {
                   className="px-3 py-2 rounded text-sm font-semibold transition-all hover:scale-105"
                   style={{ background: 'rgba(246, 70, 93, 0.1)', color: '#F6465D', border: '1px solid rgba(246, 70, 93, 0.2)' }}
                 >
-                  退出
+                  {t('logout', language)}
                 </button>
               )}
             </div>