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.

sandbox_theme.json

@@ -150,6 +150,31 @@
       "danger_hover_surface": "#3B252C",
       "danger_pressed_surface": "#4A252D"
     },
+    "ground_finish_chooser": {
+      "card_width": 880,
+      "max_height_ratio": 0.86,
+      "screen_margin": 24,
+      "choice_height": 96,
+      "choice_preview_height": 48,
+      "choice_font_size": 18,
+      "choice_min_width": 104,
+      "choice_corner_radius": 12,
+      "compact_choice_height": 50,
+      "compact_choice_preview_height": 22,
+      "compact_choice_font_size": 16,
+      "compact_grid_gap": 6,
+      "compact_layout_max_width": 600,
+      "compact_layout_max_height": 460,
+      "compact_height_ratio": 0.89,
+      "preview_height": 128,
+      "compact_preview_height": 88,
+      "preview_min_width": 224,
+      "preview_corner_radius": 12,
+      "preview_surface": "#151C28",
+      "preview_border": "#39465B",
+      "grid_gap": 8,
+      "wide_layout_min_width": 760
+    },
     "asset_selector": {
       "backdrop_alpha": 0.55,
       "cell_size": [190, 220],