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/admin.py

@@ -15,8 +15,8 @@ from .curriculum_io import parse as parse_curriculum
 from .question_io import ImportError_, export_questions, import_questions, parse
 
 from .models import (
-    Choice, Grade, Lesson, Node, NodeProgress, Question, QuestionReport, Unit, UserAnswer,
-    UserLessonCompletion,
+    Choice, Grade, Lesson, Node, NodeProgress, Question, QuestionReport, Subject, Unit,
+    UserAnswer, UserLessonCompletion,
 )
 
 
@@ -84,10 +84,18 @@ class GradeAdmin(admin.ModelAdmin):
         })
 
 
+@admin.register(Subject)
+class SubjectAdmin(admin.ModelAdmin):
+    """کتاب‌های ریاضی (ریاضی، حسابان، هندسه، …) که نوارِ جابه‌جاییِ اپ از آن‌ها ساخته می‌شود."""
+
+    list_display = ('order', 'title', 'key', 'icon', 'color')
+    ordering = ('order',)
+
+
 @admin.register(Unit)
 class UnitAdmin(admin.ModelAdmin):
-    list_display = ('id', 'title', 'grade', 'order')
-    list_filter = ('grade',)
+    list_display = ('id', 'title', 'grade', 'subject', 'order')
+    list_filter = ('grade', 'subject')
     # فیلترِ «فصل» در صفحه‌ی سوال‌ها هم از همین ترتیب می‌آید: پایه‌به‌پایه، نه
     # همه‌ی «فصل ۱»ها پشتِ هم.
     ordering = ('grade__number', 'grade_id', 'order')