The absolute public-folder base URL with a trailing slash, or an empty string when no injected view configuration is available.
The returned URL always includes a trailing slash. Append public-folder
paths without a leading slash. The URL is resolved for the current request,
so it remains correct behind proxies, tunnels, and MCP_ASSETS_URL.
Outside a synthesized browser view document, the function returns an empty string.
Return the request-resolved base URL for files in the project's
public/directory.