Add /api prefix to routes and HTTP polling fallback for WS-blocked environments

Fix API routes under /api prefix

Fix SPA serving: use StaticFiles html=True mount instead of 404 handler

Fix SPA routing: use 404 handler instead of wildcard GET to avoid clashing with POST routes

Add HF Spaces deployment

End-to-end real-time traffic analytics pipeline — YOLOv8s ONNX