Add visual harmonization tests for editor UI components and ground finish chooser

- Implemented `test_editor_visual_harmonization.gd` to validate the Stickman editor and prop editor UI layouts, ensuring proper functionality and visual consistency.
- Created `test_editor_visual_theme.gd` to verify the loading and application of visual themes in the editor, including semantic overrides and default values.
- Introduced `test_phase19_ground_finish_chooser.gd` to test the ground finish chooser's functionality, including layout responsiveness, selection behavior, and interaction with the stage.
- Added new scripts for ground finish preview and chooser UI components to enhance the editor's visual representation of ground finishes.

prop_theme.json

@@ -20,29 +20,5 @@
     "grid_size": 15,
     "background_color": "#1F1F1F",
     "grid_color": "#FFFFFF26"
-  },
-  "ui": {
-    "fonts": {
-      "body": 18,
-      "header": 24,
-      "menu": 22,
-      "menu_bar": 22,
-      "mode": 26,
-      "status": 18,
-      "prop_name": 20,
-      "context_menu": 22
-    },
-    "hit_targets": {
-      "button_min_height": 36,
-      "row_min_height": 36,
-      "mode_button_min_height": 56
-    },
-    "colors": {
-      "text": "#F2F2F2",
-      "text_muted": "#9A9A9A",
-      "border": "#FFFFFF33",
-      "accent": "#4FA3FF",
-      "inspector_background": "#262C39"
-    }
   }
 }