docs(repl): Phase 288 final documentation polish

Updated documentation for Phase 288 completion:
- docs/reference/language/repl.md: Status clarified (P0–P3 complete)
- docs/development/current/main/phases/phase-288/README.md: Added P0-P3 summaries

Changes:
- repl.md: "partial (dev tool)" → "P0–P3 complete / Phase 288.1 next"
- README.md: Each phase now has detailed description with key deliverables
- Added Box化モジュール化 (3445ef7a7) to completion record

Documentation improvements:
- ✅ P0-P3 completion clearly marked
- ✅ VMValue persistence approach documented
- ✅ Box-First modularization recorded
- ✅ Consistent with 10-Now.md, 30-Backlog.md, P1-INSTRUCTIONS.md

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude Sonnet 4.5 <noreply@anthropic.com>

docs/reference/language/repl.md

@@ -1,6 +1,6 @@
 # REPL Mode (Read–Eval–Print Loop) — Specification (SSOT)
 
-**Status**: Phase 288 MVP Implementation (2025-12-25) — partial (dev tool)
+**Status**: Phase 288 P0–P3 complete (2025-12-25, MVP) / Phase 288.1 next (session persistence + auto-display)
 
 ## Philosophy: Two Execution Contexts, One Language