🎉 feat: Phase 15.5革命完了！StringBox/IntegerBoxプラグイン優先度問題根治

何十日間の激闘ついに完全解決！"Everything is Plugin"哲学実装達成🚀

🏆 核心成果:
- FactoryPolicy システム完全実装 (StrictPluginFirst/CompatPluginFirst/BuiltinFirst)
- プラグイン優先をデフォルト化: plugins > user > builtin
- builtin_impls/ 分離実装でPhase 2削除準備完了
- unified_registry.rs でwith_env_policy()によるポリシー制御
- 環境変数制御: NYASH_BOX_FACTORY_POLICY=strict_plugin_first

🔧 技術実装:
- src/box_factory/mod.rs: FactoryPolicy enum + rebuild_cache() + policy-based ordering
- src/box_factory/builtin.rs: builtin_impls/への振り分け実装
- src/box_factory/builtin_impls/: 7ファイル分離 (削除順序コメント付き)
- src/runtime/unified_registry.rs: with_env_policy() でStrictPluginFirst デフォルト

✅ 動作確認完了:
- StringBox プラグイン優先で作成成功
- Factory Policy: StrictPluginFirst メッセージ確認
- プラグイン初期化確認 (Net plugin, FileBox plugin)

📋 Phase 2準備完了: builtin_impls/ 段階削除戦略
1. string_box.rs, integer_box.rs (プラグイン準備済み)
2. bool_box.rs (プラグイン要作成)
3. array_box.rs, map_box.rs (プラグイン確認要)
4. console_box.rs (最後 - ログ用に重要)

🎯 ChatGPT戦略 + ユーザー分離アイデアの完璧な統合実装成果！

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

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

src/box_factory/builtin_impls/console_box.rs

@@ -0,0 +1,35 @@
+/*!
+ * Builtin ConsoleBox Implementation (Phase 15.5: Scheduled for Removal)
+ *
+ * ⚠️ DEPRECATED: This will be replaced by nyash-console-plugin (exists!)
+ * 🎯 Phase 2.6: Delete this file to remove builtin ConsoleBox support (LAST)
+ */
+
+use crate::box_trait::NyashBox;
+use crate::box_factory::RuntimeError;
+
+/// Create builtin ConsoleBox instance
+///
+/// ⚠️ DEPRECATED: ConsoleBox plugin should replace this (check plugins/nyash-console-plugin)
+pub fn create(_args: &[Box<dyn NyashBox>]) -> Result<Box<dyn NyashBox>, RuntimeError> {
+    eprintln!(
+        "⚠️ [DEPRECATED] Using builtin ConsoleBox - use nyash-console-plugin!\n\
+        📋 Phase 15.5: Everything is Plugin!\n\
+        🔧 Check: plugins/nyash-console-plugin\n\
+        ⚠️ WARNING: ConsoleBox is critical for logging - remove LAST!"
+    );
+
+    Ok(Box::new(crate::boxes::console_box::ConsoleBox::new()))
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+    use crate::boxes::console_box::ConsoleBox;
+
+    #[test]
+    fn test_builtin_console_box_creation() {
+        let result = create(&[]).unwrap();
+        assert!(result.as_any().downcast_ref::<ConsoleBox>().is_some());
+    }
+}