docs(milestone): merge phase/00 pre-execution → milestone/v0.4-operator-tier

Phase 0 complete — v0.4 operator tier pre-execution artifacts:
- PROJECT.md (v0.4 scope validated, D-050..D-057)
- REQUIREMENTS.md (8 active REQs: REQ-MT-01/02, REQ-AUTH-01, REQ-DASH-01 + 4 NFRs)
- ARCHITECTURE.md (operator Postgres + auth + dashboard + aggregation + VC migration)
- PERSONAS.md (6 active personas — frontend + devops reactivated)
- RESEARCH-v0.4-operator-tier.md (7 domains, 20 risks, confidence 0.70-0.95)
- PLAN-v0.4-operator-tier.md (2 execution phases, 10 slices, 52 tasks, 8/8 REQ)
- GRILL-v0.4.md (proceed-with-conditions, 6 MUST binding decisions)

---ci---
project: praxis
phase: 0
milestone: v0.4
status: complete
requirements:
  covered: []
  partial: []
---/ci---

.ciagent/config.json

@@ -3,8 +3,8 @@
     {
       "slug": "praxis",
       "name": "Praxis",
-      "milestone": "v0.3",
-      "status": "milestone-complete"
+      "milestone": "v0.4",
+      "status": "active"
     }
   ],
   "active_project": "praxis",