docs: add Serply MCP server example

[googio]

Summary

Adds a Serply MCP server example to the mcpServers tabs in docs/config/tools.md, next to the You.com one (#575). Docs only, no code changes.

Serply exposes Google web, news, scholar, maps, jobs and video search, Bing search, URL scraping and Reddit lookups through a remote MCP server at https://api.serply.io/mcp. It authenticates with an X-Api-Key header, so the example uses headers with ${env:SERPLY_API_KEY}.

Validation

I ran the released eca-native-static-linux-amd64 0.161.2 binary as eca server --config-file with exactly the config from the new tab, then drove initialize/initialized over stdio:

• [MCP] Creating HTTP transport for server 'serply' at https://api.serply.io/mcp
• tool/serverUpdated reports serply as running with 14 tools (google_search, google_news_search, google_scholar_search, bing_search, scrape_url, ...).

The server sends no WWW-Authenticate challenge, so ECA's OAuth probe finds nothing and connects with the static header, as it does for the "Static auth header" example.

• I added a entry in changelog under unreleased section. (Docs-only, like feat: add optional You.com search integration #575, so I left CHANGELOG.md alone. Happy to add a line if you want one.)
• This is not an AI slop.

Disclosure: I work with Serply. Happy to adjust scope, naming, or drop this entirely if it isn't a direction you want for the project.

[ericdallo]

thanks!