fix(mir): Receiver used_values for DCE + trace + cleanup

- Fix: Call with Callee::Method now includes receiver in used_values()
  - Prevents DCE from eliminating Copy instructions that define receivers
  - Pattern 3 (loop_if_phi.hako) now works correctly (sum=9)

- Add: NYASH_DCE_TRACE=1 for debugging eliminated instructions
  - Shows which pure instructions DCE removes and from which block

- Cleanup: Consolidate Call used_values to single source of truth
  - Early return in methods.rs handles all Call variants
  - Removed duplicate match arm (now unreachable!())
  - ChatGPT's suggestion for cleaner architecture

- Docs: Phase 166 analysis of inst_meta layer architecture
  - Identified CSE pass callee bug (to be fixed next)
  - Improvement proposals for CallLikeInst

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

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

CLAUDE.md

@@ -36,6 +36,13 @@ NYASH_OPTION_C_DEBUG=1 cargo test --release TEST_NAME 2>&1 | grep "Option C"
 # LoopForm デバッグ
 NYASH_LOOPFORM_DEBUG=1 cargo test --release TEST_NAME 2>&1 | grep "loopform"
 
+# DCE（Dead Code Elimination）トレース ⭐NEW - 命令が消える問題のデバッグ
+NYASH_DCE_TRACE=1 ./target/release/hakorune program.hako 2>&1 | grep "\[dce\]"
+# 出力例:
+#   [dce] Eliminating unused pure instruction in bb12: %29 = Const { dst: ValueId(29), value: Void }
+#   [dce] Eliminating unused pure instruction in bb5: %38 = Copy { dst: ValueId(38), src: ValueId(36) }
+# → 「命令は emit されてるのに実行時に undefined」問題の原因特定に有効！
+
 # variable_map トレース (JoinIR PHI接続デバッグ) ⭐超重要
 NYASH_TRACE_VARMAP=1 cargo test --release TEST_NAME 2>&1 | grep "\[trace:"
 # 出力例: