OSS surfaces can now search without the hosted webclaw API. New
webclaw-fetch::search() calls Serper.dev directly with a user-supplied key
and optionally fetches + extracts the result pages. Wired into the CLI
(webclaw search, --serper-key / SERPER_API_KEY), the MCP search tool
(local-first when SERPER_API_KEY is set, cloud fallback otherwise), and the
OSS reference server (POST /v1/search). Adds futures for concurrent result
page scraping.
