docs(04): create phase plan

Phase 04: Memory & Context Management
- 4 plan(s) in 3 wave(s)
- 2 parallel, 2 sequential
- Ready for execution

.planning/ROADMAP.md

@@ -51,6 +51,12 @@ Mai's development is organized into three major milestones, each delivering dist
 - Distill long-term patterns into personality layers
 - Proactively surface relevant context from memory
 
+**Plans:** 4 plans in 3 waves
+- [ ] 04-01-PLAN.md — Storage foundation with SQLite and sqlite-vec
+- [ ] 04-02-PLAN.md — Semantic search and context-aware retrieval
+- [ ] 04-03-PLAN.md — Progressive compression and JSON archival
+- [ ] 04-04-PLAN.md — Personality learning and adaptive layers
+
 ### Phase 5: Conversation Engine
 - Multi-turn context preservation
 - Reasoning transparency and clarifying questions