complete the quiz path for grades 8 through 12, and close three gaps in the API contract

Content
-------
Every node in grades 8, 9, 10, 11 and 12 now holds a full four-question
quiz — 121 more questions, filling the two حسابان دوازدهم nodes in
فصل ۵: کاربردهای مشتق that were empty and the two ریاضی هشتم nodes that
were short. The repo's own seed guard was already failing on those two
empty nodes; it passes now.

Grades 3, 6 and 7 are the other team's books and were left alone. 39 of
their 145 nodes still hold fewer than four questions, but none is empty,
so every node on the map still plays.

An audit over all 1,593 questions in grades 8–12 found no structural
fault: no question with the wrong number of options, no question with
zero or two correct answers, no empty or duplicated option, no leftover
LaTeX, and no two identical questions inside one lesson.

Contract
--------
Three endpoints were missing or malformed in the OpenAPI schema, which
matters more than it looks: that schema is the contract the frontend
generates its client from, so a view missing there is a view the other
repo cannot call.

- NotificationMarkReadView was dropped from the schema entirely, because
  spectacular could not guess a request body for its PATCH and gives up
  on the whole view rather than the one field. It declares request=None.
- PaymentRedirectView was dropped for the same reason; it answers with a
  302 and no JSON body, which it now says.
- /api/health and /api/health/ collided on operationId and were emitted
  as health_retrieve and health_retrieve_2. The slash variant exists only
  for a monitor that calls it that way, so it is excluded from the schema.

`spectacular` now runs clean — no errors, no warnings.

Tidying
-------
Condensed the two longest comment blocks (18 and 14 lines) in
rag_verify_solutions and settings, keeping the measurement and the rule
and dropping the retelling. README gains the bulk question-authoring
workflow; the playbook's subagent section now points at the real tool
instead of describing the steps by hand.

458 tests pass.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>

config/urls.py

@@ -10,6 +10,8 @@ from django.contrib import admin
 from django.http import JsonResponse
 from django.urls import include, path
 from django.views import defaults as django_default_views
+from drf_spectacular.utils import extend_schema
+
 from config.health import HealthView
 from drf_spectacular.views import (
     SpectacularAPIView,
@@ -50,7 +52,10 @@ urlpatterns = [
     # هر `git pull` بعدی روی همین فایل گیر می‌کرد. یک مسیرِ اضافه ارزانش
     # است در برابرِ یک فایلِ دست‌کاری‌شده روی پروداکشن.
     path('api/health', HealthView.as_view(), name='health'),
-    path('api/health/', HealthView.as_view(), name='health-slash'),
+    # همان ویو، فقط برای پایشی که با اسلش صدا می‌زند. از اسکیما بیرون است تا دو
+    # مسیرِ یکسان operationIdهای health_retrieve و health_retrieve_2 نسازند.
+    path('api/health/', extend_schema(exclude=True)(HealthView).as_view(),
+         name='health-slash'),
 
     # OpenAPI schema + Swagger UI + Redoc
     path('api/schema/', SpectacularAPIView.as_view(), name='schema'),