docs: add remote search MCP configuration example

PentestAgent already supports URL-based MCP servers, but its examples do not show a credential-free option for current web search and URL extraction. This adds a copyable remote configuration while leaving the built-in Tavily tool and all defaults unchanged.

What changed

• Added a parallel-search example to mcp_examples/README.md.
• Documented the existing type: "sse" config shape and public MCP endpoint.
• Kept the setup optional and retained PentestAgent's written-authorization requirement.

Validation

• Parsed the added JSON and asserted the exact config fields.
• Verified the config maps to PentestAgent's existing POST-based remote HTTP transport.
• Completed a credential-free initialize and tools-list exchange with the endpoint, confirming web_search and web_fetch.
• Ran git diff --check and verified that only the MCP examples README changed.

Full PentestAgent startup was not run because the validation host did not have the project's declared aiohttp dependency installed.

Disclosure: I work at Parallel.ai, which operates this MCP endpoint.