Replace stale local desktop sessions in one transaction. Preserve paired clients and browser sessions, and keep the previous credential valid if replacement fails.

Closes https://github.com/pingdotgg/t3code/issues/6283.

Original implementation by seeb1337. Reviewed and verified with GPT-6 Astra (preview) in Codex.

Co-authored-by: seeb1337 <63622047+seeb1337@users.noreply.github.com>
Co-authored-by: Theo Browne <me@t3.gg>