feat add remote hand tracking backend

backend/download_model.py

@@ -0,0 +1,22 @@
+from __future__ import annotations
+
+from pathlib import Path
+from urllib.request import urlretrieve
+
+
+MODEL_URL = "https://storage.googleapis.com/mediapipe-models/hand_landmarker/hand_landmarker/float16/1/hand_landmarker.task"
+MODEL_PATH = Path(__file__).with_name("hand_landmarker.task")
+
+
+def download_model() -> None:
+    if MODEL_PATH.exists():
+        print(f"Model already exists at {MODEL_PATH}")
+        return
+
+    print("Downloading MediaPipe Hand Landmarker model...")
+    urlretrieve(MODEL_URL, MODEL_PATH)
+    print(f"Model downloaded to {MODEL_PATH}")
+
+
+if __name__ == "__main__":
+    download_model()