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/main.py

@@ -11,7 +11,7 @@ from slowapi import _rate_limit_exceeded_handler
 from slowapi.errors import RateLimitExceeded
 
 from app.limiter import limiter
-from app.routers import items, jobs, notifications, openrouter, settings
+from app.routers import items, jobs, notifications, openrouter, search, search_sites, settings
 from app.services.scheduler_service import scheduled_refresh, scheduler
 
 # Configure logging
@@ -66,6 +66,10 @@ app.mount("/screenshots", StaticFiles(directory="screenshots"), name="screenshot
 for router in [notifications.router, items.router, settings.router, jobs.router, openrouter.router]:
     app.include_router(router, prefix="/api")
 
+# Search routers (already have /api prefix)
+app.include_router(search.router)
+app.include_router(search_sites.router)
+
 
 @app.get("/api/")
 def read_root():