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/scraper/runner.py

@@ -53,6 +53,20 @@ def _save_debug_artifacts(page, product_id: int) -> tuple[Path, Path]:
     return screenshot_path, html_path
 
 
+def _update_product_from_scrape(
+    session: Session,
+    product: models.Product,
+    data: dict,
+) -> None:
+    """Met à jour le produit avec les données scrappées (titre, image)."""
+    if data.get("titre") and not product.titre:
+        product.titre = data["titre"]
+    if data.get("url_image_principale") and not product.url_image:
+        product.url_image = data["url_image_principale"]
+    session.add(product)
+    session.commit()
+
+
 def _create_snapshot(
     session: Session,
     product: models.Product,
@@ -62,6 +76,9 @@ def _create_snapshot(
     raw_json_path: Path | None,
     error_message: str | None = None,
 ) -> None:
+    # Mettre à jour le produit avec titre/image si manquants
+    _update_product_from_scrape(session, product, data)
+
     snapshot = models.ProductSnapshot(
         produit_id=product.id,
         run_scrap_id=run.id,