feat(pets): replace static cats with Live2D LittleCat model (black texture)

- Copied LittleCat model files to frontend/public/live2d/models/little-cat/
- Using the black alternate texture as default
- Created Live2DCat component that renders the model in a small canvas
- PetZone now shows a single Live2D cat instead of two SVG cats

LittleCat_Model/LittleCat_vts/items_pinned_to_model.json

@@ -0,0 +1,14 @@
+{
+    "FileMetadata": {
+        "LastSavedVTubeStudioVersion": "1.17.0",
+        "LastSavedPlatform": "Steam",
+        "LastSavedDateUTC": "Monday, 07 March 2022, 21:52:21",
+        "LastSavedDateLocalTime": "Monday, 07 March 2022, 15:52:21",
+        "LastSavedDateUnixMillisecondTimestamp": "1646689941998"
+    },
+    "SceneName": "",
+    "SceneGroupName": "",
+    "SceneModel": "",
+    "SceneID": "",
+    "Items": []
+}