fix: Enable push notifications toggle in settings

Fixed two critical issues in user settings:

1. Settings save 400 error - Removed invalid notifications boolean
   that didn't match backend DTO structure

2. Push notifications toggle not working - Properly structured
   notifications preferences as nested object with pushEnabled/emailEnabled

Changes:
- Updated state to use pushEnabled instead of simple notifications boolean
- Load pushEnabled from user.preferences.notifications.pushEnabled
- Send notifications as nested object to match UpdateProfileDto
- Both push and email notification toggles now work independently

Backend DTO expects:
{
  preferences: {
    notifications: {
      pushEnabled: boolean,
      emailEnabled: boolean
    }
  }
}

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

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

maternal-web/app/settings/page.tsx

@@ -31,7 +31,7 @@ export default function SettingsPage() {
   const [timezone, setTimezone] = useState(user?.timezone || 'UTC');
   const [timeFormat, setTimeFormat] = useState<'12h' | '24h'>(user?.preferences?.timeFormat || '12h');
   const [settings, setSettings] = useState({
-    notifications: true,
+    pushEnabled: true,
     emailUpdates: false,
     darkMode: false,
     measurementUnit: 'metric' as 'metric' | 'imperial',
@@ -45,7 +45,7 @@ export default function SettingsPage() {
   useEffect(() => {
     if (user?.preferences) {
       setSettings({
-        notifications: user.preferences.notifications ?? true,
+        pushEnabled: user.preferences.notifications?.pushEnabled ?? true,
         emailUpdates: user.preferences.emailUpdates ?? false,
         darkMode: user.preferences.darkMode ?? false,
         measurementUnit: (user.preferences.measurementUnit as 'metric' | 'imperial') || 'metric',
@@ -84,7 +84,13 @@ export default function SettingsPage() {
         photoUrl: photoUrl || undefined,
         timezone,
         preferences: {
-          ...settings,
+          notifications: {
+            pushEnabled: settings.pushEnabled,
+            emailEnabled: settings.emailUpdates,
+          },
+          emailUpdates: settings.emailUpdates,
+          darkMode: settings.darkMode,
+          measurementUnit: settings.measurementUnit,
           timeFormat,
         }
       });
@@ -235,8 +241,8 @@ export default function SettingsPage() {
               <FormControlLabel
                 control={
                   <Switch
-                    checked={settings.notifications}
-                    onChange={(e) => setSettings({ ...settings, notifications: e.target.checked })}
+                    checked={settings.pushEnabled}
+                    onChange={(e) => setSettings({ ...settings, pushEnabled: e.target.checked })}
                     disabled={isLoading}
                   />
                 }