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/development/current/main/phases/phase-288/README.md

@@ -16,10 +16,11 @@ SSOT:
 
 ## Completed (P0–P3)
 
-- P0: SSOT doc established/updated (`docs/reference/language/repl.md`)
-- P1: CLI entry point (`--repl` / `-i`)
-- P2: REPL session state isolated (Box-first; runtime-value based)
-- P3: Minimal UX and docs polish
+- ✅ **P0 (docs)**: REPL SSOT 確立 — file mode vs REPL mode 意味論、VMValue 永続化方針 (`docs/reference/language/repl.md` 336行)
+- ✅ **P1 (CLI)**: `--repl` / `-i` 起動、.help/.exit/.reset コマンド、REPL ループ実装
+- ✅ **P2 (state)**: `ReplSessionBox` (VMValue ベース) 実装、暗黙 local 許可（file mode 不変、ValueId 永続化回避）
+- ✅ **P3 (UX)**: print() 出力表示、Main box wrapper（VM entry point 修正）、.reset 実装
+- ✅ **Box化**: `src/runner/repl/` モジュール分離（ReplRunnerBox）、runner/mod.rs -118行 (commit: 3445ef7a7)
 
 ## Next (Phase 288.1)
 
@@ -30,4 +31,3 @@ The MVP intentionally deferred these:
 - Multi-line input handling (continuations)
 
 Entry: `docs/development/current/main/phases/phase-288/P1-INSTRUCTIONS.md`
-