Write the PR description for an AI-written migration

You used Claude Code to write about 80% of a TypeScript change. It moves your service's date handling from a deprecated library to the built-in Temporal API, across 14 files. You have tested the happy path locally, and 2 teammates will review it.

Write the PR description. Decide what you claim you verified, what you flag as unsure, and how you tell reviewers which parts the assistant wrote.