feat: add embed-status endpoint for per-video embedding/Qdrant detail

GET /admin/pipeline/embed-status/{video_id} returns technique pages
linked to the video, Qdrant vector count, and last stage 6 event —
provides data for the currently non-functional Embed tab in admin UI.

backend/routers/pipeline.py

@@ -1306,6 +1306,78 @@ async def reindex_all(
     }
 
 
+# ── Admin: Embedding status ──────────────────────────────────────────────────
+
+@router.get("/admin/pipeline/embed-status/{video_id}")
+async def get_embed_status(
+    video_id: str,
+    db: AsyncSession = Depends(get_session),
+):
+    """Get embedding/indexing status for a video's technique pages.
+
+    Returns which technique pages have been embedded, vector counts from
+    Qdrant, and the last stage 6 event timestamp.
+    """
+    from models import KeyMoment
+
+    # Get technique pages linked to this video's key moments
+    moments = (await db.execute(
+        select(KeyMoment.technique_page_id)
+        .where(KeyMoment.source_video_id == video_id)
+        .where(KeyMoment.technique_page_id.isnot(None))
+        .distinct()
+    )).scalars().all()
+
+    page_ids = set(moments)
+    pages_info = []
+    if page_ids:
+        rows = (await db.execute(
+            select(TechniquePage.id, TechniquePage.title, TechniquePage.slug)
+            .where(TechniquePage.id.in_(page_ids))
+        )).all()
+        pages_info = [{"id": str(r.id), "title": r.title, "slug": r.slug} for r in rows]
+
+    # Get last stage 6 event for this video
+    last_embed_event = (await db.execute(
+        select(PipelineEvent.created_at, PipelineEvent.event_type)
+        .where(PipelineEvent.video_id == video_id)
+        .where(PipelineEvent.stage == "stage6_embed_and_index")
+        .order_by(PipelineEvent.created_at.desc())
+        .limit(1)
+    )).first()
+
+    # Try to get Qdrant vector count for this video
+    qdrant_count = None
+    try:
+        from config import get_settings
+        from pipeline.qdrant_client import QdrantManager
+        from qdrant_client.models import Filter, FieldCondition, MatchValue
+
+        settings = get_settings()
+        qdrant = QdrantManager(settings)
+        result = qdrant._client.count(
+            collection_name=qdrant._collection,
+            count_filter=Filter(
+                must=[FieldCondition(key="source_video_id", match=MatchValue(value=video_id))]
+            ),
+            exact=True,
+        )
+        qdrant_count = result.count
+    except Exception:
+        pass
+
+    return {
+        "video_id": video_id,
+        "technique_pages": pages_info,
+        "technique_page_count": len(pages_info),
+        "qdrant_vector_count": qdrant_count,
+        "last_embed_event": {
+            "created_at": last_embed_event.created_at.isoformat(),
+            "event_type": last_embed_event.event_type,
+        } if last_embed_event else None,
+    }
+
+
 # ── Admin: Creator profile editing ───────────────────────────────────────────
 
 @router.put("/admin/pipeline/creators/{creator_id}")