Security review fixes: admin permissions, guest sessions, payment edge cases, assistant leaks

- Admin: refund/cancel/mark-resolved/Bazaar-link actions need change permission; question and
  curriculum import need add/delete; content browser needs view_question; guest device ids are
  shown to superusers only.
- Accounts: registering a guest's phone revokes the guest's earlier sessions; self-deletion keeps
  Redemption, UserOffer and the phone's OTP rows; the public demo guest cannot be deleted
  (DEMO_GUEST_DEVICE_IDS); display-name contact filter covers any separator and social handles.
- Payment: callback without Authority is 400; a second Bazaar purchase on a paid order is 409;
  orders snapshot credits/hearts/days at creation (payment.0011).
- Assistant: a broken diagram no longer makes a streamed answer free; a late off-topic marker
  refuses the answer (not stored, not cached); a disconnect saves the partial answer; only
  KNOWN_COLLECTIONS are searched.
- Infra: secret-key file is created atomically (workers no longer split keys); no default
  INTERNAL_SERVICE_KEY; Kavenegar key and Bazaar token kept out of error logs; Swagger/ReDoc
  pinned; schema throttled; docker compose bound to 127.0.0.1; non-ASCII digit ids are 400;
  ticket text capped at 5000.
- docs/security-before-production.md: remaining open items 24-31 and the guard tests.

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

CLAUDE.md

@@ -65,7 +65,9 @@ default hosts/CORS/cache/secret key (`/api/health` warns); `LocMemCache` without
 OAuth path beside the Pishkhan token (server still uses OAuth); `birthYear` alone in
 `PATCH /api/user/profile` (frontend type still allows it); `totalQuestions` accepted but
 ignored (frontend sends it); orders with no `plan_id` from before 2026-09-25 (none
-paid on the server on 2026-10-03).
+paid on the server on 2026-10-03); orders without the `question_credits`/`hearts_days`/
+`duration_days` snapshot (`payment.0011`) grant and refund from the plan's current values;
+`DEMO_GUEST_DEVICE_IDS` defaults to `frontend-test-device` (remove with the demo data).
 
 ## Before any real user: read `docs/security-before-production.md`