GlobalWatcher::add returns Ok(None) while the native watch-limit
cooldown is active, and FsWatcher::add_existing_path treated that as
success: the path was never watched, with no retry and no error. A
long-lived watch (like a repository's git directory) that happened to
register during a cooldown window silently never received events.

Route the skipped registration through the existing pending-path
machinery, which already polls until registration succeeds and emits a
rescan event for the path so that changes missed in the interim are
picked up.

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Release Notes:

- N/A or Added/Fixed/Improved ...