File-size decomposition (no behavior change). Move getLoggedInActorKey,
getSessionActorKey, and ensureWatchHistoryExtensionPermissions (which depend only
on imported singletons, not module state) into js/watchHistoryActorHelpers.js, and
drop the now-unused getActiveSigner/requestDefaultExtensionPermissions/getApplication
imports from the service.
watchHistoryService.js: 1491 -> 1388 lines (below its original 1395 baseline;
re-recorded to 1386 to lock the reduction).
Build + full unit suite green.
Co-Authored-By: Claude Opus 4.8 <[email protected]>
