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>

config/settings.py

@@ -227,7 +227,14 @@ STORAGES = {
         'BACKEND': 'django.core.files.storage.FileSystemStorage',
     },
     'staticfiles': {
-        'BACKEND': 'whitenoise.storage.CompressedManifestStaticFilesStorage',
+        # عمداً نسخه‌ی Manifest نیست: اون نسخه اگه staticfiles.json نباشه
+        # (یعنی هر وقت collectstatic اجرا نشده) موقعِ رندرِ هر صفحه‌ی ادمین
+        # ValueError پرت می‌کنه. این یعنی تست‌ها می‌شکستن — جنگو در تست همیشه
+        # DEBUG=False می‌کنه، پس WHITENOISE_USE_FINDERS هم خاموشه — و مهم‌تر،
+        # روزی که روی سرور DEBUG=0 بشه و collectstatic فراموش بشه، پنلِ ادمین
+        # کاملاً می‌خوابید. این نسخه فقط فشرده‌سازی می‌کنه و هیچ‌وقت fail نمی‌شه؛
+        # بهاش از دست دادنِ hash در نامِ فایله که برای پنلِ ادمین ناچیزه.
+        'BACKEND': 'whitenoise.storage.CompressedStaticFilesStorage',
     },
 }
 # با DEBUG=1، از finders مستقیم سرو می‌کنه؛ نیازی به collectstatic نیست.