DesktopController is a route root that had grown a controller's worth of
session-list plumbing inline. Extract the cohesive fetch/paging cluster into
a focused hook and a tested pure helper, per AGENTS.md's "keep route roots
thin" guidance:
- use-session-list-actions.ts: refreshSessions / loadMoreSessions /
loadMoreSessionsForProfile / loadMoreMessagingForPlatform / refreshCronJobs
(plus the private cron/messaging refreshers, sessionsToKeep, and the
excluded-source constants)
- desktop-controller-utils.ts: pure sameCronSignature helper (+ unit tests)
Pure restructuring, no behavior change. desktop-controller.tsx: 1,441 -> 1,233.
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