draw a diagram in tutor answers: validated JSON from the model, rendered by the app; add the fourth companion tedi

The model ends a shape question with <diagram>{json}</diagram>; rag/services/diagram.py
splits it off before mathtext, validates it against a whitelist and stores it on
Message.diagram (ai_tutor.0006). It reaches the app in the SSE done event and in
conversation history. Prompt tutor-v6-diagrams; a hint next to the question (shape
words only) raised gpt-4.1-mini from 3/12 to 12/12 diagrams, 0/8 on arithmetic.

progress.0005 adds tedi (600 xp) to the companion catalog.

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

progress/tests.py

@@ -255,3 +255,14 @@ class RebuildLeaderboardCommandTests(TestCase):
         call_command('rebuild_leaderboard', '--period', 'all_time', '--dry-run', verbosity=0)
 
         self.assertEqual(LeaderboardEntry.objects.count(), 0)
+
+
+class FourCompanionsCatalogTests(TestCase):
+    """migrationهای 0004 و 0005: سه‌یار و تدی همان چهار slugی‌اند که فرانت می‌شناسد."""
+
+    def test_catalog_has_the_four_companions_in_order(self):
+        rows = list(
+            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)])