public user IDs, plans priced by tutor cost, age-based tutor tone, self-service account deletion

- profile publicId ("User482917", accounts/public_id.py); admin shows and searches it
- plans API reports aiDailyQuota per plan and freeAiDailyQuota; migration 0007 sets the
  temporary prices (monthly 99,000 / yearly 990,000 toman, 5 tutor questions a day) unless
  an admin already edited the yearly plan
- tutor tone follows the learner's age (18+ gets an adult tone at any grade); notation
  still follows the grade's book; answer cache keyed by tone (prompt tutor-v12-age-tone)
- POST /api/user/delete: phone users confirm with a fresh SMS code (same checks as login,
  now shared in verify_phone_otp), guests type "حذف"; payment records are kept, demo
  accounts refused
- delete_users --skip-paid

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

config/settings.py

@@ -475,6 +475,8 @@ REST_FRAMEWORK = {
         'discount_validate': '20/hour',
         'discount_redeem': '10/hour',
         'user_profile_write': '60/hour',
+        # حذفِ حساب با کدِ پیامکی؛ سقفِ حدسِ کد جدا در verify_phone_otp است.
+        'account_delete': '5/hour',
         'affiliate_track': '10/hour',
         'payment_webhook': '60/hour',
         'payment_pay': '30/hour',