fix(extraction): index C++ pure virtual methods as nodes (#1727) (#1758)

Pure-virtual declarations (`virtual int read(int key) = 0;`) parse as
field_declaration, not function_definition, so they minted no method node —
calls through an abstract base and cpp-override synthesis had nothing to
attach to. Mirror Java interface methods: mint the node (TS + kernel), mark
isAbstract, and cover with extraction/e2e/parity fixtures.

Co-authored-by: Colby McHenry <colbymchenry@users.noreply.github.com>

__tests__/fixtures/kernel-parity/torture.cpp

@@ -39,6 +39,8 @@ class Session {
 public:
   void open();
   virtual ~Session() {}
+  // #1727 — pure virtual must mint a method node (parity between wasm + kernel).
+  virtual int read(int key) = 0;
 };
 void Session::open() {}
 }  // namespace app::net