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/seed_sync.py

@@ -27,6 +27,7 @@ import json
 from django.db import transaction
 
 from . import question_io
+from .curriculum_io import _subject_or_error
 from .models import Grade, Lesson, Node, Question, SeedRecord, Unit
 
 
@@ -91,7 +92,10 @@ def sync(grades: list[dict], question_rows: list[dict]) -> dict:
                 if ledger.delivered(_key('unit', *upath)):
                     counts['retired'] += 1
                     continue
-                unit = Unit.objects.create(grade=grade, title=u['title'], order=u['order'])
+                unit = Unit.objects.create(
+                    grade=grade, title=u['title'], order=u['order'],
+                    subject=_subject_or_error(u['subject']),
+                )
                 counts['units'] += 1
             ledger.record(_key('unit', *upath), 'unit')
             if u.get('blurb') and not unit.blurb: