Grades 4 and 5, Bazaar purchase from the app, pack SKUs

- rag: MATH_4 / MATH_5 textbooks (TOC and page offsets read from the PDFs)
- content: grades 4 and 5 in the seed files: 7 units / 28 nodes each,
  204 + 194 questions (every node >= 4), all re-solved blind once
- subscription: Plan.bazaar_sku (admin); POST /api/subscription/purchase
  accepts paymentMethod=bazaar for packs, rejects unknown methods (was ignored)
- payment: idempotency key cannot switch provider; discount codes refused
  on Bazaar orders (Bazaar charges the fixed SKU price)

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

content/management/commands/seed_curriculum_from_textbook.py

@@ -27,6 +27,9 @@ from rag.services.config import build_collection_name
 from rag.services.textbooks import TEXTBOOKS, get_textbook
 
 GRADE_STYLE = {
+    # چهارم/پنجم (۲۰۲۶-۱۰-۰۳): رنگ‌های گرمِ روشن، کنارِ سبزِ ششم، تا سه پایه‌ی دبستان یک خانواده باشند.
+    'چهارم': ('grade-4', '#FFB300'),
+    'پنجم': ('grade-5', '#FF7043'),
     'ششم': ('grade-6', '#4CAF50'),
     'هفتم': ('grade-7', '#2196F3'),
     'هشتم': ('grade-8', '#9C27B0'),