feat: Add multi-site product search system with SearXNG integration

This commit adds a comprehensive product search feature that allows users
to search for products across multiple configured e-commerce sites.

Backend changes:
- Add SearXNG service to docker-compose for meta-search capability
- Add SearchSite model and Alembic migration with default sites
- Create searxng_service.py for search queries across sites
- Create light_scraper_service.py for fast HTTP-based extraction
- Create search_service.py orchestrator combining SearXNG + HTTP + Browserless
- Add API endpoints for search (/api/search) with SSE streaming
- Add CRUD endpoints for search sites (/api/search-sites)

Frontend changes:
- Add new /search page with real-time results display
- Create SearchResultCard component for product display
- Add Progress, Checkbox, and Badge UI components
- Update Settings page with search sites management section
- Add navigation link to search page
- Create new modern SVG logo with price-flow gradient design
- Update favicon to SVG format

The search system uses a hybrid approach:
1. SearXNG finds product URLs across configured sites
2. Light HTTP scraper attempts fast extraction
3. Falls back to Browserless for JavaScript-heavy sites
4. Results stream progressively via SSE

app/models.py

@@ -77,3 +77,19 @@ class Settings(Base):
 
     key = Column(String, primary_key=True, index=True)
     value = Column(Text)
+
+
+class SearchSite(Base):
+    """Sites configurés pour la recherche de produits"""
+    __tablename__ = "search_sites"
+
+    id: int = Column(Integer, primary_key=True, index=True)  # type: ignore
+    name: str = Column(String, nullable=False)  # type: ignore  # "Amazon France"
+    domain: str = Column(String, unique=True, nullable=False, index=True)  # type: ignore  # "amazon.fr"
+    logo_url: str | None = Column(String, nullable=True)  # type: ignore
+    category: str | None = Column(String, nullable=True)  # type: ignore  # "Tech", "Déco", "Généraliste"
+    is_active: bool = Column(Boolean, default=True)  # type: ignore
+    priority: int = Column(Integer, default=0)  # type: ignore  # Ordre d'affichage
+    requires_js: bool = Column(Boolean, default=False)  # type: ignore  # Force Browserless si True
+    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