Mirrors Phase 1's coexistence test pattern. Verifies:
- The coexistence group (group_fusion_show_when_enterprise_absent)
exists and is referenceable
- The reports engine model (fusion.report.engine) is always
registered, regardless of Enterprise install state
- The Financial Reports root menu requires the coexistence group
- The Open Report... sub-menu (period picker wizard) is gated too
Uses V19 group_ids attribute with a graceful fallback to groups_id for
older runtime variants.
Tests: 3 new (test_coexistence.py). Net 115 -> 118.
Made-with: Cursor
