Playwright recorder

For a page on this origin, paste its URL and load. For a different host/port (e.g. http://localhost:4700), paste that URL and click Load: it is rewritten to /recorder/upstream on this server, which reverse-proxies to http://127.0.0.1:4700 (override with env RECORDER_PROXY_TARGET). That keeps the iframe same-origin so clicks are visible to the recorder. Generated Playwright tests should use this proxied base URL. Steps store a CSS path from body; codegen errors if a path cannot be computed. HTTP log lists fetch and XMLHttpRequest from the preview (not static assets unless loaded via JS).