Subjects per grade (math, calculus, geometry, stats, discrete), 5 new textbooks, 202 new islands, long islands split, hand-written figures and lesson texts for the new books

- content.Subject + Unit.subject, /api/home?subject=, tutor grounded in the chosen book
- 5 new books ingested; ~1150 hand-written questions, islands named by hand
- node_split: islands over 7 lessons split into parts of <=6 (lesson ids and progress kept)
- Lesson.figures hand-authored and visually checked for 653 lessons of the new books;
  gen_lesson_figures got --subject and survives network errors
- seed files re-exported

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

content/management/commands/seed_curriculum_from_textbook.py

@@ -21,7 +21,7 @@
 from django.core.management.base import BaseCommand, CommandError
 from django.db import transaction
 
-from content.models import Grade, Lesson, Node, Unit
+from content.models import Grade, Lesson, Node, Subject, Unit
 from rag.models import LessonChunk
 from rag.services.config import build_collection_name
 from rag.services.textbooks import TEXTBOOKS, get_textbook
@@ -179,11 +179,17 @@ class Command(BaseCommand):
             title=grade_title, defaults={'icon': icon, 'color': color},
         )
 
+        # کتاب باید در جدولِ Subject باشد (migrationِ 0015 پنج‌تایی را می‌سازد؛ کتابِ تازه از ادمین).
+        subject = Subject.objects.filter(title=book.subject).first()
+        if subject is None:
+            raise CommandError(
+                f'کتابِ «{book.subject}» در جدولِ Subject نیست؛ از ادمین (محتوا ← کتاب‌ها) بسازید.'
+            )
         counts = {'units': 0, 'nodes': 0, 'lessons': 0}
         for chapter, groups in plan:
             unit, _ = Unit.objects.update_or_create(
                 grade=grade, title=chapter.title,
-                defaults={'order': chapter.number},
+                defaults={'order': chapter.number, 'subject': subject},
             )
             counts['units'] += 1