fixed theme selection

frontend/src/App.tsx

@@ -218,7 +218,7 @@ const App: React.FC = () => {
     localStorage.setItem('theme', newTheme);
     if (user) {
         try {
-            await api.patch('users/update_theme/', { theme: newTheme });
+            await api.patch('users/update_preferences/', { theme: newTheme });
         } catch (err) {
             console.error('Failed to update theme on server');
         }

frontend/src/pages/Settings.tsx

@@ -212,7 +212,7 @@ const Settings: React.FC<SettingsProps> = ({ themeName, onThemeChange }) => {
                         <Divider />
                         
                         <ListSubheader>Dark Themes</ListSubheader>
-                        <MenuItem value="mocha">Mocha (Default)</MenuItem>
+                        <MenuItem value="mocha">Mocha</MenuItem>
                         <MenuItem value="frappe">Frappé</MenuItem>
                         <MenuItem value="macchiato">Macchiato</MenuItem>
                         <MenuItem value="atom">Atom One Dark</MenuItem>