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/l10n/app_localizations_zh.dart

@@ -1159,6 +1159,18 @@ class AppLocalizationsZh extends AppLocalizations {
 
   @override
   String get settingsInviteInvalidCode => '请输入有效的6位邀请码';
+
+  @override
+  String get settingsDoNotSellTitle => '个性化广告推荐';
+
+  @override
+  String get settingsDoNotSellDescription => '关闭后，我们不会将您的个人信息用于广告推荐';
+
+  @override
+  String get settingsDoNotSellEnabled => '已关闭';
+
+  @override
+  String get settingsDoNotSellDisabled => '已开启';
 }
 
 /// The translations for Chinese, using the Han script (`zh_Hant`).
@@ -2072,4 +2084,16 @@ class AppLocalizationsZhHant extends AppLocalizationsZh {
 
   @override
   String get settingsInviteInvalidCode => '請輸入有效的6位邀請碼';
+
+  @override
+  String get settingsDoNotSellTitle => '個人化廣告推薦';
+
+  @override
+  String get settingsDoNotSellDescription => '關閉後，我們不會將您的個人資訊用於廣告推薦';
+
+  @override
+  String get settingsDoNotSellEnabled => '已關閉';
+
+  @override
+  String get settingsDoNotSellDisabled => '已開啟';
 }