new app — cleaned-up RAG pipeline (Qdrant retrieval + GPT), ported from Rag_backend

Self-contained app; wired into settings/urls in the next commit. Data
stays in the parallel team's live Qdrant — nothing is copied into our DB.

apps.py
  - RagConfig.
models.py
  - LessonChunk: DB-of-record for one summarized lesson chunk
    (original_text + summary + embedding_vector) mirrored as a single
    Qdrant point; loose lesson_id/grade_id ints, no cross-app FK.
    LessonChunkImage for future multimodal lessons.
migrations/0001_initial.py
  - initial tables for the two models.
services/clients.py
  - lazy, lru_cache'd OpenAI + Qdrant clients (Rag_backend builds them at
    import time and crashes without keys). RagNotConfigured raised when a
    key/lib is missing; Qdrant client uses check_compatibility=False for
    the 1.19-client / 1.17-server minor version gap.
services/config.py
  - rag_is_configured(), collection-name template, grade-title resolution
    (RAG_GRADE_TITLE_OVERRIDES -> content.Grade.title), retrieval top-k.
services/known_collections.py
  - exact live Qdrant catalog: 6 collection names, math chapter-number ->
    exact "فصل N: ..." string tables per (subject, grade), and the
    علوم/اجتماعی lesson-number -> title maps. filter_key_for_subject()
    picks `chapter` for math, `lesson_number` otherwise;
    resolve_math_chapter() maps a plain chapter number (Persian or Latin
    digits) to the stored string.
services/embedding.py
  - embed_text() pinned to OPENAI_EMBEDDING_MODEL (text-embedding-3-small,
    1536d) so vectors match the other team's existing collections.
services/chunking.py
  - split_text_into_chunks(), summarize_chunk() (gpt-4o-mini, JSON out);
    plain exceptions instead of ninja HttpError.
services/qdrant_store.py
  - ensure_collection(), upsert_points(), search(): the lesson filter
    matches the value both as str and native, since Qdrant stores
    lesson_number as int and chapter as string.
services/retrieval.py
  - resolve_target() -> (collection, filter_key, filter_value), reused by
    the cache key and debug block.
  - retrieve_context() -> (chunks, meta): embed -> Qdrant search scoped to
    one lesson/chapter -> top-k. Math payloads (no `summary`) fall back to
    generalSolution/problem/solution; a 404 collection returns empty.
services/generation.py
  - generate_answer() and stream_answer() (token iterator for SSE);
    context-grounded Persian prompt that explains from retrieved text
    rather than refusing.
services/pdf.py
  - textbook PDF -> page images -> gpt-4o vision problem-type extraction
    (adapted from Rag_backend mathapp); returns dicts, no on-disk JSON.
    pymupdf/pdf2image optional — missing libs raise RagNotConfigured.
services/ingest.py
  - ingest_text() / ingest_pdf(): chunk -> summarize -> embed -> persist
    LessonChunk + upsert Qdrant, in one transaction.
services/answer_cache.py
  - short-TTL cache of the final answer keyed by
    sha1(collection | filter_value | normalized-question).
services/tutor.py
  - thin answer_question() (retrieve -> generate) for direct callers.
serializers.py, urls.py, views.py
  - POST /api/rag/ingest/text, POST /api/rag/ingest/pdf (HasInternalServiceKey,
    throttle scope rag_ingest), GET /api/rag/chunks review list.
    RagProviderUnavailable -> clean 503.
admin.py
  - LessonChunk admin with an inline for its images.
management/commands/rag_catalog.py
  - read-only live Qdrant listing (--values, --json); never writes.
tests.py
  - mocked-client tests: ask-with-retrieval, ingest, SSE stream, answer
    cache, and rag_is_configured() gating.

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

rag/services/config.py

@@ -0,0 +1,44 @@
+"""
+هم‌خوانیِ نامِ collection و کلیدِ فیلترِ Qdrant با دادهٔ موجودِ تیمِ دیگر.
+
+در Rag_backend نامِ collection این‌طور ساخته می‌شه:
+    f"{subject.name} {subject.grade.title}".lower()
+و فیلترِ درس با کلیدِ payloadِ "lesson_number" (برای درس‌های متنی) یا
+"chapter" (برای ریاضی) انجام می‌شه. اینجا هر دو از settings قابلِ تنظیم‌ان
+چون اسمِ دقیقِ گرید حساسه (کاربر قبلاً با اسمِ نادرست به مشکل خورده بود).
+"""
+from django.conf import settings
+
+
+def rag_is_configured() -> bool:
+    return bool(
+        settings.OPENAI_API_KEY
+        and settings.QDRANT_API_KEY
+        and not settings.RAG_FORCE_MOCK
+    )
+
+
+def resolve_grade_title(grade_id, fallback: str = '') -> str:
+    """gradeId → عنوانِ گرید همان‌طور که در نامِ collectionِ تیمِ دیگه اومده."""
+    overrides = getattr(settings, 'RAG_GRADE_TITLE_OVERRIDES', {}) or {}
+    if grade_id in overrides:
+        return str(overrides[grade_id])
+    if grade_id is not None:
+        try:
+            from content.models import Grade
+
+            grade = Grade.objects.filter(pk=grade_id).only('title').first()
+            if grade is not None:
+                return grade.title
+        except Exception:
+            pass
+    return fallback
+
+
+def build_collection_name(subject: str, grade_title: str) -> str:
+    template = getattr(settings, 'RAG_COLLECTION_NAME_TEMPLATE', '{subject} {grade}')
+    return template.format(subject=(subject or '').strip(), grade=(grade_title or '').strip()).lower()
+
+
+def retrieval_top_k() -> int:
+    return int(getattr(settings, 'RAG_RETRIEVAL_TOP_K', 4))