docs(repl): Phase 288 documentation cleanup

Updated documentation to reflect actual implementation status:
- docs/reference/language/repl.md: Corrected examples (variable persistence TODO)
- docs/development/current/main/10-Now.md: Phase 288 completion noted
- docs/development/current/main/30-Backlog.md: Updated with Phase 288.1 tasks
- docs/development/current/main/phases/phase-288/: Added phase documentation

Accurate REPL behavior examples:
- x = 1 works (implicit local)
- print(x) errors (persistence in Phase 288.1)
- Expression auto-display deferred

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

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

docs/development/current/main/10-Now.md

@@ -2,10 +2,10 @@
 
 ## Current Focus (next)
 
-- Phase 287（stabilization）: ビルド/テスト軽量化（quick が重すぎる）
-  - 目的: `tools/smokes/v2/run.sh --profile quick` を「開発中に回せる速さ」に戻す（意味論不変、分類/配置で解決）
-  - 入口: `docs/development/current/main/phases/phase-287/README.md`
-  - 手順: `docs/development/current/main/phases/phase-287/P1-INSTRUCTIONS.md`
+- Phase 288.1（dev-tools）: REPL session persistence + auto-display
+  - 目的: `hakorune --repl` で変数が行を跨いで生きる（暗黙local）＋式の自動表示（`_` を含む）
+  - 入口: `docs/development/current/main/phases/phase-288/README.md`
+  - 手順: `docs/development/current/main/phases/phase-288/P1-INSTRUCTIONS.md`
 
 - Phase 284（design-first）: Return as ExitKind SSOT（patternに散らさない）
   - 目的: `return` を `ExitKind` + `compose::*` / `emit_frag()` に収束させ、pattern側の個別実装を増やさない