Three new test files:
- sidebar-monitoring-reorg.test.ts: asserts monitoring has 4 children (activity item + logs/audit/system groups), no costs-parameters group, no logs-activity in items
- sidebar-costs-section.test.ts: asserts costs section exists with 4 items in correct order, costs removed from analytics, costs positioned between analytics and monitoring
- sidebar-back-compat.test.ts: asserts activity added + logs-activity preserved in HIDEABLE_SIDEBAR_ITEM_IDS, admin preset shows activity and hides logs-activity (B30)
