keep ingested chunks findable and structured

Two bugs made self-ingested content useless, both silently:

- _payload wrote `chapter_number` (int) while math retrieval filters on
  `chapter` (the full "فصل ۲: کسر" string), so anything we ingest could
  never match a search — no error, just permanently invisible content.
- ingest_pdf flattened the vision extraction into one text blob and threw
  away type/keywords/generalSolution/problem/solution. LessonChunk is the
  source of truth, so rebuilding meant paying for vision again — and the
  problem/solution pairs are the input for building lesson questions.

LessonChunk now stores those fields and _payload emits them under the same
keys the other team's collections use, so ours and theirs stay one shape.

Also fixes a regression from the whitenoise commit: the Manifest storage
variant raises when staticfiles.json is absent, which broke all 23 admin
rendering tests (Django forces DEBUG=False in tests, so USE_FINDERS is off)
and would have taken the admin panel down entirely the day DEBUG=0 ships
without a collectstatic run.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>

rag/migrations/0002_lessonchunk_chapter_title_and_more.py

@@ -0,0 +1,48 @@
+# Generated by Django 5.2.17 on 2026-09-10 12:24
+
+from django.db import migrations, models
+
+
+class Migration(migrations.Migration):
+
+    dependencies = [
+        ('rag', '0001_initial'),
+    ]
+
+    operations = [
+        migrations.AddField(
+            model_name='lessonchunk',
+            name='chapter_title',
+            field=models.CharField(blank=True, max_length=255),
+        ),
+        migrations.AddField(
+            model_name='lessonchunk',
+            name='general_solution',
+            field=models.TextField(blank=True),
+        ),
+        migrations.AddField(
+            model_name='lessonchunk',
+            name='grade_title',
+            field=models.CharField(blank=True, max_length=100),
+        ),
+        migrations.AddField(
+            model_name='lessonchunk',
+            name='keywords',
+            field=models.JSONField(blank=True, default=list),
+        ),
+        migrations.AddField(
+            model_name='lessonchunk',
+            name='problem',
+            field=models.TextField(blank=True),
+        ),
+        migrations.AddField(
+            model_name='lessonchunk',
+            name='problem_type',
+            field=models.CharField(blank=True, max_length=255),
+        ),
+        migrations.AddField(
+            model_name='lessonchunk',
+            name='solution',
+            field=models.TextField(blank=True),
+        ),
+    ]