docs(15-01): complete consolidation data model plan

- Add 15-01-SUMMARY.md with task commits, decisions, and next phase readiness
- Update STATE.md with decisions and session position
- Update ROADMAP.md phase 15 progress (1/2 plans complete)
- Mark requirement RPT-04 complete in REQUIREMENTS.md

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

.planning/STATE.md

@@ -2,15 +2,15 @@
 gsd_state_version: 1.0
 milestone: v2.3
 milestone_name: Tenant Management & Report Enhancements
-status: roadmap-ready
-stopped_at: roadmap created — ready for phase 15 planning
-last_updated: "2026-04-09"
+status: planning
+stopped_at: Completed 15-01-PLAN.md
+last_updated: "2026-04-09T09:42:37.151Z"
 last_activity: 2026-04-09 — Roadmap created for v2.3 (phases 15-19)
 progress:
   total_phases: 5
   completed_phases: 0
-  total_plans: 0
-  completed_plans: 0
+  total_plans: 2
+  completed_plans: 1
 ---
 
 # Project State
@@ -61,6 +61,8 @@ Decisions are logged in PROJECT.md Key Decisions table.
 - Group expansion (Phase 17) calls Graph at export time, not at scan time — scan pipeline unchanged
 - Auto-take ownership uses PnP `Tenant.SetSiteAdmin` — requires Tenant Admin scope
 - App registration must be atomic with rollback; partial Entra state is worse than no state
+- [Phase 15]: MakeKey declared internal for test access via InternalsVisibleTo without exposing as public API
+- [Phase 15]: LINQ GroupBy+Select for consolidation merge instead of mutable dictionary — consistent with functional codebase style
 
 ### Pending Todos
 
@@ -72,7 +74,7 @@ None.
 
 ## Session Continuity
 
-Last session: 2026-04-09
-Stopped at: Roadmap created — ready to plan Phase 15
+Last session: 2026-04-09T09:42:37.149Z
+Stopped at: Completed 15-01-PLAN.md
 Resume file: None
 Next step: `/gsd:plan-phase 15`