docs: handbook, diagrams and guides brought up to 2026-10-02

- technical-handbook: question packs instead of subscriptions, real
  hearts with the new wait screen (screenshot), math-only tutor and what
  is charged (new 9-7), admin cancel/refund, Bazaar planId, account
  deletion, 59 endpoints, 779 tests, 14 apps, status and open decisions.
- Diagrams redrawn: use-case (buy a pack, refunds), data model
  (QuestionCredit, HeartsPass, Profile.birth_date), pack payment sequence.
- The PDF is now built from the Markdown by docs/build_handbook.py
  (pandoc + Chrome, font in docs/assets); the hand-made HTML it used to
  come from was not in the repo and had been lost.
- architecture, operations, security-before-production (item 13 closed),
  ai-cost-and-guardrails and README follow the same changes.

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

README.md

@@ -12,8 +12,8 @@
 | **وضعیت** | روی پروداکشن، در حالِ سرویس‌دهی |
 | **آدرسِ زنده** | `https://mathapi.tadrisino2.ir` · [سلامت](https://mathapi.tadrisino2.ir/api/health) |
 | **استک** | Python 3.11+ · Django 5.2 · DRF · SQLite · Qdrant (RAG) |
-| **API** | ۶۱ اندپوینت · مستنداتِ زنده در `/api/docs/` |
-| **تست** | ۶۸۵ تست، همه سبز (`python manage.py test`) |
+| **API** | ۵۹ اندپوینت · مستنداتِ زنده در `/api/docs/` |
+| **تست** | ۷۷۹ تست، همه سبز (`python manage.py test`) |
 | **محتوا** | ۸ پایه · ۵۸ فصل · ۲۶۳ نود · ۲٬۶۱۷ درس · ۲٬۵۴۵ سوال |
 
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