docs: add dependency migration example with Parallel MCP

[georgeatparallel]

Summarize dependency migrations with excerpts from a public migration guide or release-notes page using Parallel Search MCP. The opt-in example connects over HTTP without a Parallel account or API key, keeps the configured LLM provider, and includes the source URL in its output. Run it after building smart-diff, passing a repository, commit range and documentation URL.

Documentation excerpts are bounded, and retrieval failures stop the example. The library and CLI keep their existing dependencies and behavior.

I work at Parallel.

[codecov-commenter]

Codecov Report

✅ All modified and coverable lines are covered by tests.

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[mcarvin8]

Thanks for the contribution! LGTM