feat: auto-scrape on product creation and update product data (Step 4)

- Add automatic scraping when creating a new product
- Update product title and image from scraped data
- Add GET /products/{id}/snapshots endpoint for price history
- Add list_snapshots and get_latest_snapshot to CRUD

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

backend/app/db/crud.py

@@ -43,3 +43,22 @@ def update_product(db: Session, product: models.Product, changes: schemas.Produc
 def remove_product(db: Session, product: models.Product) -> None:
     db.delete(product)
     db.commit()
+
+
+def list_snapshots(db: Session, product_id: int, limit: int = 30) -> list[models.ProductSnapshot]:
+    return (
+        db.query(models.ProductSnapshot)
+        .filter(models.ProductSnapshot.produit_id == product_id)
+        .order_by(models.ProductSnapshot.scrape_le.desc())
+        .limit(limit)
+        .all()
+    )
+
+
+def get_latest_snapshot(db: Session, product_id: int) -> models.ProductSnapshot | None:
+    return (
+        db.query(models.ProductSnapshot)
+        .filter(models.ProductSnapshot.produit_id == product_id)
+        .order_by(models.ProductSnapshot.scrape_le.desc())
+        .first()
+    )