Sprint 2 Step 1: base ASTNode class and Module concept

Adds the C++ editor stack foundation with ASTNode (id, conceptType, parent pointer, virtual dtor) and Module as the first concrete concept (name, targetLanguage). Header-only, compiles with C++20, test passes all assertions.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

editor/src/ast/Module.h

@@ -0,0 +1,15 @@
+#pragma once
+#include "ASTNode.h"
+
+class Module : public ASTNode {
+public:
+    std::string name;
+    std::string targetLanguage;
+
+    Module() { conceptType = "Module"; }
+    Module(const std::string& id, const std::string& name, const std::string& lang)
+        : name(name), targetLanguage(lang) {
+        this->id = id;
+        this->conceptType = "Module";
+    }
+};