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

docs/protocols/profile/profile-protocol.md

@@ -51,8 +51,19 @@ Response:
       "timezone": "Asia/Shanghai",
       "country": "CN"
     },
-    "privacy": {},
-    "notification": {}
+    "privacy": {
+      "can_sell": false,
+      "profile_visibility": "public"
+    },
+    "notification": {
+      "allow_notifications": true,
+      "allow_vibration": true
+    },
+    "divination_tutorial": {
+      "divination_entry_shown": false,
+      "auto_divination_shown": false,
+      "manual_divination_shown": false
+    }
   },
   "updated_at": "2026-04-05T12:34:56+00:00"
 }
@@ -105,7 +116,10 @@ Request:
       "timezone": "Asia/Shanghai",
       "country": "CN"
     },
-    "privacy": {},
+    "privacy": {
+      "can_sell": false,
+      "profile_visibility": "public"
+    },
     "notification": {
       "allow_notifications": true,
       "allow_vibration": true
@@ -125,6 +139,19 @@ Rules:
 - Additional fields are forbidden.
 - `divination_tutorial` tracks user's tutorial completion state for divination flows.
 
+### Privacy settings
+
+| Field | Type | Default | Description |
+|-------|------|---------|-------------|
+| `can_sell` | `bool` | `false` | Whether user's personal info can be used for personalized ads. `false` = opt-out (privacy protective default). |
+| `profile_visibility` | `str` | `"public"` | Profile visibility level. Reserved for future use. |
+
+**Compatibility note:**
+
+- Previous versions used `privacy: {}` (empty object). This has been upgraded to a structured `PrivacySettings` schema.
+- Strategy: `backward-compatible` — old `privacy: {}` payloads are accepted and normalized to default `PrivacySettings()`.
+- Migration: No client action required; backend normalizes empty/missing privacy to defaults.
+
 Response:
 
 - Returns the same shape as `GET /users/me/profile`.