Add integration tests for User Feed API

New tests for:
- getUserFeeds, getFeed, getUserDefaultFeedId
- createFeed, createFeedDuplicateNameFails
- updateFeed, updateFeedNotOwnerFails
- deleteFeed, deleteFeedDefaultFails
- duplicateFeed, duplicateFeedDuplicateNameFails
- feedGeneratorsPerFeed, feedCountsAccurate

Also updated activateFollowList, deactivateFollowList, and
getActiveFollowLists API methods to support optional feedId parameter.

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>