Initial snapshot: hand motion pipeline (Dyn-HaMR + dex-retargeting + SPIDER)

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

third_party/hamer/fetch_demo_data.sh

@@ -0,0 +1,7 @@
+# Google drive link to download the model
+gdown https://drive.google.com/uc?id=1mv7CUAnm73oKsEEG1xE3xH2C_oqcFSzT
+
+# Alternatively, you can use wget
+#wget https://www.cs.utexas.edu/~pavlakos/hamer/data/hamer_demo_data.tar.gz
+
+tar --warning=no-unknown-keyword --exclude=".*" -xvf hamer_demo_data.tar.gz