feat: Replace DuckDuckGo with direct site search

- Remove duckduckgo-search dependency (unreliable results)
- Add direct_search_service.py that scrapes sites' search pages directly
- Add search_url and product_link_selector fields to SearchSite model
- Add beautifulsoup4 and lxml for HTML parsing
- Update schemas with new fields
- Add database migration for new columns

Direct search is more reliable as it queries each site's own search
functionality instead of relying on external search engines.

app/models.py

@@ -92,5 +92,7 @@ class SearchSite(Base):
     priority: int = Column(Integer, default=0)  # type: ignore  # Ordre d'affichage
     requires_js: bool = Column(Boolean, default=False)  # type: ignore  # Force Browserless si True
     price_selector: str | None = Column(String, nullable=True)  # type: ignore  # Sélecteur CSS pour le prix
+    search_url: str | None = Column(String, nullable=True)  # type: ignore  # URL de recherche avec {query} placeholder
+    product_link_selector: str | None = Column(String, nullable=True)  # type: ignore  # Sélecteur CSS pour les liens produits
     created_at: datetime = Column(DateTime, default=lambda: datetime.now(UTC))  # type: ignore
     updated_at: datetime = Column(DateTime, default=lambda: datetime.now(UTC), onupdate=lambda: datetime.now(UTC))  # type: ignore