Document the common-ai MCPHook

[Lee-W]

MCPHook was the only hook in the provider without a page of its own, so the transports it supports, the connection fields it reads, and its relationship to MCPToolset could only be learned by reading the source. The MCP connection page also left out the timeout extra field, even though one of its own examples already sets it.

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Generated-by: [Claude] following the guidelines

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