v2.1.22

v2.1.22: fix concurrent site refresh race conditions

- cleanupOldPages skips cleanup when browserRefCount > 1 to prevent
  closing pages used by other concurrent detection tasks
- fetchWithBrowserFallback retries with a new page when sharedPage is
  closed by another task (Target closed / Session closed)
- Replace detectingSite (singular string) with isDetecting (boolean)
  computed from detectingSites (Set) for independent per-site spinner
- refreshMessage setTimeout checks site name before clearing to prevent
  timer race between concurrent refreshes