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.cpp

@@ -5,7 +5,8 @@
 #include "PyObjectUtils.h"
 #include "PyVector.h"
 #include "PyPositionHelper.h"
-#include "UIDrawable_methods.h"
+// UIDrawable methods now in UIBase.h
+#include "UIEntityPyMethods.h"
 
 
 UIEntity::UIEntity() 
@@ -383,7 +384,8 @@ PyGetSetDef UIEntity::getsetters[] = {
     {"sprite_number", (getter)UIEntity::get_spritenumber, (setter)UIEntity::set_spritenumber, "Sprite index on the texture on the display (deprecated: use sprite_index)", NULL},
     {"x", (getter)UIEntity::get_float_member, (setter)UIEntity::set_float_member, "Entity x position", (void*)0},
     {"y", (getter)UIEntity::get_float_member, (setter)UIEntity::set_float_member, "Entity y position", (void*)1},
-    UIDRAWABLE_GETSETTERS,
+    {"visible", (getter)UIEntity_get_visible, (setter)UIEntity_set_visible, "Visibility flag", NULL},
+    {"opacity", (getter)UIEntity_get_opacity, (setter)UIEntity_set_opacity, "Opacity (0.0 = transparent, 1.0 = opaque)", NULL},
     {NULL}  /* Sentinel */
 };