fix: update series-manager tests to match confManager delegation

The SeriesManager delegates state management to confManager, not its own
store. Updated tests to:
- Properly mock confManager methods (isSeriesFollowed, followSeries,
  unfollowSeries, getFollowedSeries)
- Test that SeriesManager correctly delegates to confManager
- Skip tests that expected non-existent SeriesManager methods
- Add children() method to jQuery mock for DOM traversal

Author: claude