[Draft] feat: test Yarn v6#4063

Draft

Saadnajmi wants to merge 7 commits intomicrosoft:mainfrom

Saadnajmi:migrate-yarn-v6

Commits on Mar 9, 2026

Migrate to Yarn v6 (rc.15) via Yarn Switch

Saadnajmi
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claude
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ci: install Yarn Switch in CI workflows

Saadnajmi
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claude
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ci: fix Windows Yarn Switch shell, TS1540 skipLibCheck, and remove --immutable

Saadnajmi
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claude
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Commits on Mar 10, 2026