Fixes #235: [Fleet Execution] [GitPatch Automate Improvements Example]

[davideast]

Fixes #235

Adds a new practical SDK example gitpatch-improve demonstrating how to query recent sessions for ChangeSetArtifact data, extract the GitPatch (unidiffPatch), and use it in a new repoless session to analyze and identify areas for code improvement.
Updates the core README.md to link to the new example.

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PR created automatically by Jules for task 7070919864024976256 started by @davideast

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