feat: Implement privacy preferences for users and agents with new database field, service methods, and API endpoints.

prisma/schema.prisma

@@ -104,6 +104,7 @@ model User {
 
   // User Preferences
   notificationPreferences Json? // { email: {...}, push: {...} }
+  privacyPreferences      Json? // { privacySettings: {...}, dataSettings: {...} }
 
   // Timestamps
   createdAt         DateTime     @default(now())