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/migrations/0015_seed_subjects.py

@@ -0,0 +1,24 @@
+from django.db import migrations
+
+# رنگ‌ها جدا از رنگِ پایه‌ها (Grade.color) و از هم‌اند تا دکمه‌های نوارِ کتاب‌ها در نقشه
+# به‌چشم یک مسیرِ جدا بیایند. آیکون‌ها نامِ lucide‌اند (همان فهرستی که نقشه می‌شناسد).
+SUBJECTS = [
+    ('math', 'ریاضی', 'Sigma', '#ED6956', 1),
+    ('calculus', 'حسابان', 'LineChart', '#00BCD4', 2),
+    ('geometry', 'هندسه', 'Compass', '#9B7BFF', 3),
+    ('stats', 'آمار و احتمال', 'BarChart3', '#FF7A3D', 4),
+    ('discrete', 'گسسته', 'Network', '#5FBF8F', 5),
+]
+
+
+def create_subjects(apps, schema_editor):
+    Subject = apps.get_model('content', 'Subject')
+    for key, title, icon, color, order in SUBJECTS:
+        Subject.objects.get_or_create(
+            key=key, defaults={'title': title, 'icon': icon, 'color': color, 'order': order},
+        )
+
+
+class Migration(migrations.Migration):
+    dependencies = [('content', '0014_subject')]
+    operations = [migrations.RunPython(create_subjects, migrations.RunPython.noop)]