feat(mir): Phase 25.1f完了 - Conservative PHI + ControlForm観測レイヤー

🎉 Conservative PHI Box理論による完全SSA構築

**Phase 7-B: Conservative PHI実装**
- 片方branchのみ定義変数に対応（emit_void使用）
- 全変数にPHI生成（Conservative Box理論）
- Stage-1 resolver全テスト緑化（3/3 PASS）

**Phase 25.1f: ControlForm観測レイヤー**
- LoopShape/IfShape/ControlForm構造定義
- Loop/If統一インターフェース実装
- debug_dump/debug_validate機能追加
- NYASH_CONTROL_FORM_TRACE環境変数対応

**主な変更**:
- src/mir/builder/phi.rs: Conservative PHI実装
- src/mir/control_form.rs: ControlForm構造（NEW）
- src/mir/loop_builder.rs: LoopForm v2デフォルト化

**テスト結果**:
✅ mir_stage1_using_resolver_min_fragment_verifies
✅ mir_stage1_using_resolver_full_collect_entries_verifies
✅ mir_parserbox_parse_program2_harness_parses_minimal_source

🤖 Generated with Claude Code
Co-Authored-By: Claude <noreply@anthropic.com>
Co-Authored-By: ChatGPT <chatgpt@openai.com>

src/runner/hv1_inline.rs

@@ -129,18 +129,17 @@ pub fn run_json_v1_inline(json: &str) -> i32 {
 
                 let sval = regs.get(&src).cloned();
                 let is_integer = sval.is_some(); // hv1 inline stores i64 only → integer
-                let mut out = 0i64;
                 if operation == "check" || operation == "is" {
-                    if target == "i64" || target == "int" || target == "integer" {
-                        out = if is_integer { 1 } else { 0 };
+                    let out: i64 = if target == "i64" || target == "int" || target == "integer" {
+                        if is_integer { 1 } else { 0 }
                     } else if target == "bool" {
                         // Inline model uses integer registers; treat 0/1 as bool when present
-                        out = if let Some(v) = sval { if v == 0 || v == 1 { 1 } else { 0 } } else { 0 };
+                        if let Some(v) = sval { if v == 0 || v == 1 { 1 } else { 0 } } else { 0 }
                     } else if target == "string" {
-                        out = 0; // no string registers in inline model
+                        0 // no string registers in inline model
                     } else {
-                        out = 0;
-                    }
+                        0
+                    };
                     regs.insert(dst, out);
                 } else {
                     // cast/as: pass-through (MVP)