Fix overlay sizing by using size_hint=None

The UIManager was overriding the overlay rect set by UIDropdown.do_layout
because size_hint=(0, 0) caused it to be resized to 0x0. Using
size_hint=None prevents the UIManager from touching the size.

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

Author: benjamin-kirkbride

arcade/gui/widgets/dropdown.py

@@ -26,7 +26,9 @@ class _UIDropdownOverlay(UIFocusMixin, UIBoxLayout):
 
     def __init__(self, max_height: float = 200):
         # Horizontal layout: [scroll_area | scroll_bar]
-        super().__init__(vertical=False, align="top", size_hint=(0, 0))
+        # size_hint=None prevents UIManager from overriding the rect
+        # that UIDropdown.do_layout explicitly sets.
+        super().__init__(vertical=False, align="top", size_hint=None)
         self._max_height = max_height
 
         self._options_layout = UIBoxLayout(size_hint=(1, 0))