public: publish selfhost snapshot to public repo (SSOT using + AST merge + JSON VM fixes)

- SSOT using profiles (aliases/packages via nyash.toml), AST prelude merge
- Parser/member guards; Builder pin/PHI and instance→function rewrite (dev on)
- VM refactors (handlers split) and JSON roundtrip/nested stabilization
- CURRENT_TASK.md updated with scope and acceptance criteria

Notes: dev-only guards remain togglable via env; no default behavior changes for prod.

src/instance_v2.rs

@@ -245,9 +245,7 @@ impl InstanceBox {
                 .unwrap()
                 .insert(field_name.to_string(), value.clone());
 
-            // fields_ngにも同期
-            // 一時的にNullを設定（型変換が複雑なため）
-            // TODO: SharedNyashBox -> NyashValueの適切な変換を実装
+            // fields_ngにも同期（暫定: Null で占位）
             self.fields_ng
                 .lock()
                 .unwrap()