docs: mention connectors in MCP guide

[seratch]

Summary

• add a Connectors section to the MCP guide after the tool filtering content
• link to the connectors example repository code and the platform connector guide
• localize the new section for the Japanese MCP guide

Testing

• pnpm lint

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https://chatgpt.com/codex/tasks/task_i_68be9dac67b08320aa6bd57124481f52

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