Interactive in-browser canvas for real-time preview of HTML, React components, SVGs, and diagrams with SSE hot-reload

掌上 dsh — the standalone mobile surface for the dsh web GUI: scan-to-pair device trust, the /m/ phone UI, the /m/api RPC channel with realtime SSE mux bridge, and a polished desktop pairing panel. Extracted from dsh-remote-web-ui (M1, behavior-identical)