chore: Phase 25.2関連ドキュメント更新＆レガシーテストアーカイブ整理

## ドキュメント更新
- CURRENT_TASK.md: Phase 25.2完了記録
- phase-25.1b/e/q/25.2 README更新
- json_v0_bridge/README.md新規追加

## テストファイル整理
- vtable_*テストをtests/archive/に移動（6ファイル）
- json_program_loop.rsテスト追加

## コード整理
- プラグイン（egui/python-compiler）微修正
- benchmarks.rs, instance_v2.rs更新
- MIR関連ファイル微調整

## 全体成果
Phase 25.2完了により：
- LoopSnapshotMergeBox統一管理実装
- ValueId(1283)バグ根本解決
- ~35行コード削減（目標210行の16%）
- 11テスト全部PASS、3実行テストケースPASS

tests/json_program_loop.rs

@@ -0,0 +1,98 @@
+use serde_json::json;
+use std::collections::HashMap;
+
+fn verify_program(label: &str, program: serde_json::Value) {
+    let src = serde_json::to_string(&program).expect("serialize program");
+    let module = nyash_rust::runner::json_v0_bridge::parse_json_v0_to_module_with_imports(
+        &src,
+        HashMap::new(),
+    )
+    .unwrap_or_else(|e| panic!("{}: failed to parse Program(JSON): {}", label, e));
+
+    let mut verifier = nyash_rust::mir::verification::MirVerifier::new();
+    if let Err(errors) = verifier.verify_module(&module) {
+        panic!(
+            "{}: MIR verification failed with errors: {:?}",
+            label, errors
+        );
+    }
+}
+
+fn program_simple_loop() -> serde_json::Value {
+    json!({
+        "version": 0,
+        "kind": "Program",
+        "body": [
+            { "type": "Local", "name": "loopCount", "expr": { "type": "Int", "value": 0 } },
+            {
+                "type": "Loop",
+                "cond": { "type": "Bool", "value": true },
+                "body": [
+                    { "type": "Break" }
+                ]
+            },
+            { "type": "Return", "expr": { "type": "Var", "name": "loopCount" } }
+        ]
+    })
+}
+
+fn program_loop_with_continue() -> serde_json::Value {
+    json!({
+        "version": 0,
+        "kind": "Program",
+        "body": [
+            { "type": "Local", "name": "cycles", "expr": { "type": "Int", "value": 0 } },
+            {
+                "type": "Loop",
+                "cond": { "type": "Bool", "value": true },
+                "body": [
+                    { "type": "Local", "name": "loopTick", "expr": { "type": "Int", "value": 1 } },
+                    {
+                        "type": "If",
+                        "cond": { "type": "Bool", "value": true },
+                        "then": [
+                            { "type": "Continue" }
+                        ],
+                        "else": [
+                            { "type": "Break" }
+                        ]
+                    }
+                ]
+            },
+            { "type": "Return", "expr": { "type": "Var", "name": "cycles" } }
+        ]
+    })
+}
+
+fn program_loop_body_local_exit() -> serde_json::Value {
+    json!({
+        "version": 0,
+        "kind": "Program",
+        "body": [
+            {
+                "type": "Loop",
+                "cond": { "type": "Bool", "value": true },
+                "body": [
+                    { "type": "Local", "name": "bodyTemp", "expr": { "type": "Int", "value": 42 } },
+                    { "type": "Break" }
+                ]
+            },
+            { "type": "Return", "expr": { "type": "Var", "name": "bodyTemp" } }
+        ]
+    })
+}
+
+#[test]
+fn json_loop_simple_verifies() {
+    verify_program("json_loop_simple", program_simple_loop());
+}
+
+#[test]
+fn json_loop_with_continue_verifies() {
+    verify_program("json_loop_with_continue", program_loop_with_continue());
+}
+
+#[test]
+fn json_loop_body_local_exit_verifies() {
+    verify_program("json_loop_body_local_exit", program_loop_body_local_exit());
+}