docs: add tenancy module migration plan and session notes
DOCUMENTATION:
- docs/architecture/tenancy-module-migration.md
- Complete migration plan for tenancy module
- Files to migrate: routes, services, models, schemas
- Files to keep in root (framework level)
- Files for other modules (messaging, cms, monitoring, core)
- Target module structure
- Recommended migration order
- docs/proposals/SESSION_NOTE_2026-01-31_tenancy-module-consolidation.md
- Session summary and key decisions
- Module ownership assignments
- Next actions and priorities
Key principle: Tenancy owns identity and organizational hierarchy.
Everything else belongs to feature modules.
Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>