feat(privacy): add personalized ads toggle in settings

- Add PrivacySettings schema with can_sell field (default: false)
- Move privacy toggle to GeneralSettingsScreen with clear labeling
- Update l10n for zh/en/zh_hant with user-friendly copy
- Clean up redundant PrivacyNotificationSettingsScreen
- Update profile-protocol.md to reflect new privacy schema
- Fix basedpyright warnings in user.py

apps/lib/features/settings/data/apis/profile_api.dart

@@ -46,7 +46,10 @@ class ProfileApi {
           'timezone': settings.preferences.timezone,
           'country': settings.preferences.country,
         },
-        'privacy': settings.privacy,
+        'privacy': {
+          'can_sell': settings.privacy.canSell,
+          'profile_visibility': settings.privacy.profileVisibility,
+        },
         'notification': {
           'allow_notifications': settings.notification.allowNotifications,
           'allow_vibration': settings.notification.allowVibration,
@@ -115,6 +118,17 @@ class ProfileApi {
           )
         : const PreferenceSettings();
 
+    final privacyRaw = settingsRaw is Map<String, dynamic>
+        ? settingsRaw['privacy']
+        : null;
+    final privacy = privacyRaw is Map<String, dynamic>
+        ? PrivacySettings(
+            canSell: (privacyRaw['can_sell'] as bool?) ?? false,
+            profileVisibility:
+                (privacyRaw['profile_visibility'] as String?) ?? 'public',
+          )
+        : const PrivacySettings();
+
     final notificationRaw = settingsRaw is Map<String, dynamic>
         ? settingsRaw['notification']
         : null;
@@ -150,10 +164,7 @@ class ProfileApi {
       avatarPath: json['avatar_path'] as String?,
       avatarUrl: json['avatar_url'] as String?,
       preferences: preferences,
-      privacy: settingsRaw is Map<String, dynamic>
-          ? (settingsRaw['privacy'] as Map<String, dynamic>? ??
-                const <String, dynamic>{})
-          : const <String, dynamic>{},
+      privacy: privacy,
       notification: notification,
       divinationTutorial: divinationTutorial,
     );