fix: prevent segfault when closing window via X button

- Add cleanup() method to GameEngine to clear Python references before destruction
- Clear timers and McRFPy_API references in proper order
- Call cleanup() at end of run loop and in destructor
- Ensure cleanup is only called once per GameEngine instance

Also includes:
- Fix audio ::stop() calls (already in place, OpenAL warning is benign)
- Add Caption support for x, y keywords (e.g. Caption("text", x=5, y=10))
- Refactor UIDrawable_methods.h into UIBase.h for better organization
- Move UIEntity-specific implementations to UIEntityPyMethods.h

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

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

src/UIEntity.h

@@ -51,6 +51,11 @@ public:
     bool setProperty(const std::string& name, int value);
     bool getProperty(const std::string& name, float& value) const;
     
+    // Methods that delegate to sprite
+    sf::FloatRect get_bounds() const { return sprite.get_bounds(); }
+    void move(float dx, float dy) { sprite.move(dx, dy); position.x += dx; position.y += dy; }
+    void resize(float w, float h) { /* Entities don't support direct resizing */ }
+    
     static PyObject* at(PyUIEntityObject* self, PyObject* o);
     static PyObject* index(PyUIEntityObject* self, PyObject* Py_UNUSED(ignored));
     static PyObject* die(PyUIEntityObject* self, PyObject* Py_UNUSED(ignored));