diagrams for every grade, sectioned prompt, repair of real model slips; fill lesson texts and thin islands

Diagrams: 14 kinds drawn by the app (plane with constructed points, graphs with
computed roots/extrema/tangents, number lines with intervals, solids, charts,
tables, Venn, mapping, trees, fractions, grids, groups, clock). The catalog is
split by topic and only the matching sections go next to a question (200-1073
tokens instead of 1854). parse() repairs slips seen on 96 real book problems:
Persian digits in JSON numbers, 2*pi, // comments, bare items, Venn with
Persian set names. Measured: 45/48 valid on the second round, 0/8 on plain
arithmetic; visual review of 83: 64 right, 3 weak, 16 wrong.

Content: 82 new questions so no island has fewer than four; fill_lesson_texts
writes Unit.blurb (58) and Lesson.example/steps (590) from verified book
problems, never the lesson's own quiz problem. seed_content only fills empty
fields, so admin edits survive a deploy. Tedi unlocks at 500 xp.

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

progress/tests.py

@@ -265,4 +265,4 @@ class FourCompanionsCatalogTests(TestCase):
             Character.objects.filter(slug__in=['sigma', 'delta', 'pi', 'tedi'])
             .order_by('order').values_list('slug', 'unlock_xp')
         )
-        self.assertEqual(rows, [('sigma', 0), ('delta', 100), ('pi', 300), ('tedi', 600)])
+        self.assertEqual(rows, [('sigma', 0), ('delta', 100), ('pi', 300), ('tedi', 500)])