refactor(plan): Phase 273 P3+ - Legacy code removal

Phase 273 P3+ 完成: レガシーコード削除 + 未使用 import 整理

Removed Legacy Items:
1. emit_scan_with_init_edgecfg() - Pattern6 固有の emission 関数
   - File deleted: src/mir/builder/emission/loop_scan_with_init.rs (~144 lines)
   - Replaced by: generalized Frag API (Phase 273 P2)

2. CoreCarrierInfo struct - Legacy carrier representation
   - Removed from: src/mir/builder/control_flow/plan/mod.rs (~15 lines)
   - Replaced by: CorePhiInfo (generalized PHI representation)

3. verify_carrier() function - CoreCarrierInfo validator
   - Removed from: src/mir/builder/control_flow/plan/verifier.rs (~15 lines)
   - Replaced by: generalized PHI verification (V7-V9)

Code Cleanup:
- cargo fix applied: unused imports removed (~30 files)
- Verifier invariants updated: V1→V2-V9 (carrier→PHI model)
- Module declaration cleanup in emission/mod.rs

Impact:
- Total lines removed: ~174 lines (net reduction)
- Pattern-agnostic architecture strengthened
- All legacy Pattern6 references eliminated

Tests:
- ✅ VM tests PASS (phase254/256/258)
- ✅ LLVM tests PASS (phase256/258)

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

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

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

@@ -3,8 +3,8 @@
 ## Current Focus (next)
 
 - Phase 273（design-first）: `docs/development/current/main/phases/phase-273/README.md`
-  - P1: DomainPlan→CorePlan（固定語彙）+ PlanNormalizer（SSOT）+ PlanVerifier（fail-fast）で “増殖” を止める
-    - CorePlan は `Seq/Loop/If/Effect/Exit` のみ（scan専用 Effect/variant 禁止、式を String にしない）
+  - P3 proposal: generalized CoreLoopPlan を SSOT 化して legacy fallback を撤去（収束の完成）
+    - 指示書: `docs/development/current/main/phases/phase-273/P3-CLAUDE.md`
 
 ## Recently Completed (2025-12-22)
 
@@ -15,6 +15,7 @@
 - Phase 278 P0（deprecated PHI env vars removal）: `docs/development/current/main/phases/phase-278/README.md`
 - Phase 279 P0（type propagation pipeline SSOT unification）: `docs/development/current/main/phases/phase-279/README.md`
 - Phase 273 P0（Plan Extractor PoC）: `docs/development/current/main/phases/phase-273/README.md`
+- Phase 273 P1/P2（Domain→Core→Lowerer + Pattern7移行）: `docs/development/current/main/phases/phase-273/README.md`
 
 ---