Fix critical issues: script loading, entity types, and color properties

- Issue #37: Fix Windows scripts subdirectory not checked
  - Updated executeScript() to use executable_path() from platform.h
  - Scripts now load correctly when working directory differs from executable

- Issue #76: Fix UIEntityCollection returns wrong type
  - Updated UIEntityCollectionIter::next() to check for stored Python object
  - Derived Entity classes now preserve their type when retrieved from collections

- Issue #9: Recreate RenderTexture when resized (already fixed)
  - Confirmed RenderTexture recreation already implemented in set_size() and set_float_member()
  - Uses 1.5x padding and 4096 max size limit

- Issue #79: Fix Color r, g, b, a properties return None
  - Implemented get_member() and set_member() in PyColor.cpp
  - Color component properties now work correctly with proper validation

- Additional fix: Grid.at() method signature
  - Changed from METH_O to METH_VARARGS to accept two arguments

All fixes include comprehensive tests to verify functionality.

closes #37, closes #76, closes #9, closes #79

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

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

src/UIEntity.cpp

@@ -119,6 +119,10 @@ int UIEntity::init(PyUIEntityObject* self, PyObject* args, PyObject* kwds) {
     else
         self->data = std::make_shared<UIEntity>(*((PyUIGridObject*)grid)->data);
 
+    // Store reference to Python object
+    self->data->self = (PyObject*)self;
+    Py_INCREF(self);
+
     // TODO - PyTextureObjects and IndexTextures are a little bit of a mess with shared/unshared pointers
     self->data->sprite = UISprite(texture_ptr, sprite_index, sf::Vector2f(0,0), 1.0);
     self->data->position = pos_result->data;